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Lightning parameters of engineering interest Application of lightning
detection technologies
Vladimir A Rakov
Department of Electrical and Computer Engineering
University of Florida Gainesville
EGAT Bangkok Thailand
November 7 2012
Lightning parameters of engineering interest Application of lightning detection technologies
1 CIGRE Working Group C4407 activities 2 General characterization of lightning 3 Ground flash density 4 Number of strokes per flash 5 Multiple channel terminations on ground 6 Rocket-triggered lightning 7 Lightning peak current distributions
8 Calibration of lightning locating systems
9 Summary
3
1 CIGRE Working Group C4407 activities
4 4
CIGRE Working Group C4407 activities
The CIGRE Working Group C4407 Lightning Parameters for Engineering Applications was formed in April 2008 The target date for completion of its work was originally set at March 31 2011 It is presently extended to December 31 2012 The final meeting was held in conjunction with the ICLP 2012 in Vienna Austria (Sept 2 2012) The final product of this WG is the Reference Document a summary of which may be published in the Electra
Members of CIGRE WG C4-407 Lightning Parameters for Engineering Applications A Borghetti (Secretary) Italy C Bouquegneau Belgium W Chisholm Canada V Cooray Sweden K Cummins USA G Diendorfer Austria F Heidler Germany A Hussein Canada M Ishii Japan CA Nucci Italy A Piantini Brazil O Pinto Brazil X Qie China F Rachidi Switzerland V Rakov (Convener) USA M Saba Brazil T Shindo Japan W Schulz Austria R Thottappillil Sweden S Visacro Brazil W Zischank (Corresponding Member) Germany
WG Scope
bull Evaluation of current measurements on instrumented towers
bull Evaluation of current measurements for rocket-triggered lightning
bull Evaluation of the procedures used to estimate lightning currents from measured fields with emphasis on those implemented in lightning locating systems
bull Inclusion of additional lightning parameters (eg characteristics of continuing currents return-stroke propagation speed equivalent lightning channel impedance etc) that are presently not on the CIGRE list but needed in engineering applications
bull Further characterization of positive and bipolar lightning discharges
bull Characterization of upward lightning discharges
bull Search for any geographical seasonal and other variations in lightning parameters
bull Preparation of a reference document ldquoLightning Parameters for Engineering Applicationsrdquo based on the current understanding of lightning processes and taking into account limitations of various measuring techniques
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Lightning parameters of engineering interest Application of lightning detection technologies
1 CIGRE Working Group C4407 activities 2 General characterization of lightning 3 Ground flash density 4 Number of strokes per flash 5 Multiple channel terminations on ground 6 Rocket-triggered lightning 7 Lightning peak current distributions
8 Calibration of lightning locating systems
9 Summary
3
1 CIGRE Working Group C4407 activities
4 4
CIGRE Working Group C4407 activities
The CIGRE Working Group C4407 Lightning Parameters for Engineering Applications was formed in April 2008 The target date for completion of its work was originally set at March 31 2011 It is presently extended to December 31 2012 The final meeting was held in conjunction with the ICLP 2012 in Vienna Austria (Sept 2 2012) The final product of this WG is the Reference Document a summary of which may be published in the Electra
Members of CIGRE WG C4-407 Lightning Parameters for Engineering Applications A Borghetti (Secretary) Italy C Bouquegneau Belgium W Chisholm Canada V Cooray Sweden K Cummins USA G Diendorfer Austria F Heidler Germany A Hussein Canada M Ishii Japan CA Nucci Italy A Piantini Brazil O Pinto Brazil X Qie China F Rachidi Switzerland V Rakov (Convener) USA M Saba Brazil T Shindo Japan W Schulz Austria R Thottappillil Sweden S Visacro Brazil W Zischank (Corresponding Member) Germany
WG Scope
bull Evaluation of current measurements on instrumented towers
bull Evaluation of current measurements for rocket-triggered lightning
bull Evaluation of the procedures used to estimate lightning currents from measured fields with emphasis on those implemented in lightning locating systems
bull Inclusion of additional lightning parameters (eg characteristics of continuing currents return-stroke propagation speed equivalent lightning channel impedance etc) that are presently not on the CIGRE list but needed in engineering applications
bull Further characterization of positive and bipolar lightning discharges
bull Characterization of upward lightning discharges
bull Search for any geographical seasonal and other variations in lightning parameters
bull Preparation of a reference document ldquoLightning Parameters for Engineering Applicationsrdquo based on the current understanding of lightning processes and taking into account limitations of various measuring techniques
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
3
1 CIGRE Working Group C4407 activities
4 4
CIGRE Working Group C4407 activities
The CIGRE Working Group C4407 Lightning Parameters for Engineering Applications was formed in April 2008 The target date for completion of its work was originally set at March 31 2011 It is presently extended to December 31 2012 The final meeting was held in conjunction with the ICLP 2012 in Vienna Austria (Sept 2 2012) The final product of this WG is the Reference Document a summary of which may be published in the Electra
Members of CIGRE WG C4-407 Lightning Parameters for Engineering Applications A Borghetti (Secretary) Italy C Bouquegneau Belgium W Chisholm Canada V Cooray Sweden K Cummins USA G Diendorfer Austria F Heidler Germany A Hussein Canada M Ishii Japan CA Nucci Italy A Piantini Brazil O Pinto Brazil X Qie China F Rachidi Switzerland V Rakov (Convener) USA M Saba Brazil T Shindo Japan W Schulz Austria R Thottappillil Sweden S Visacro Brazil W Zischank (Corresponding Member) Germany
WG Scope
bull Evaluation of current measurements on instrumented towers
bull Evaluation of current measurements for rocket-triggered lightning
bull Evaluation of the procedures used to estimate lightning currents from measured fields with emphasis on those implemented in lightning locating systems
bull Inclusion of additional lightning parameters (eg characteristics of continuing currents return-stroke propagation speed equivalent lightning channel impedance etc) that are presently not on the CIGRE list but needed in engineering applications
bull Further characterization of positive and bipolar lightning discharges
bull Characterization of upward lightning discharges
bull Search for any geographical seasonal and other variations in lightning parameters
bull Preparation of a reference document ldquoLightning Parameters for Engineering Applicationsrdquo based on the current understanding of lightning processes and taking into account limitations of various measuring techniques
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
4 4
CIGRE Working Group C4407 activities
The CIGRE Working Group C4407 Lightning Parameters for Engineering Applications was formed in April 2008 The target date for completion of its work was originally set at March 31 2011 It is presently extended to December 31 2012 The final meeting was held in conjunction with the ICLP 2012 in Vienna Austria (Sept 2 2012) The final product of this WG is the Reference Document a summary of which may be published in the Electra
Members of CIGRE WG C4-407 Lightning Parameters for Engineering Applications A Borghetti (Secretary) Italy C Bouquegneau Belgium W Chisholm Canada V Cooray Sweden K Cummins USA G Diendorfer Austria F Heidler Germany A Hussein Canada M Ishii Japan CA Nucci Italy A Piantini Brazil O Pinto Brazil X Qie China F Rachidi Switzerland V Rakov (Convener) USA M Saba Brazil T Shindo Japan W Schulz Austria R Thottappillil Sweden S Visacro Brazil W Zischank (Corresponding Member) Germany
WG Scope
bull Evaluation of current measurements on instrumented towers
bull Evaluation of current measurements for rocket-triggered lightning
bull Evaluation of the procedures used to estimate lightning currents from measured fields with emphasis on those implemented in lightning locating systems
bull Inclusion of additional lightning parameters (eg characteristics of continuing currents return-stroke propagation speed equivalent lightning channel impedance etc) that are presently not on the CIGRE list but needed in engineering applications
bull Further characterization of positive and bipolar lightning discharges
bull Characterization of upward lightning discharges
bull Search for any geographical seasonal and other variations in lightning parameters
bull Preparation of a reference document ldquoLightning Parameters for Engineering Applicationsrdquo based on the current understanding of lightning processes and taking into account limitations of various measuring techniques
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Members of CIGRE WG C4-407 Lightning Parameters for Engineering Applications A Borghetti (Secretary) Italy C Bouquegneau Belgium W Chisholm Canada V Cooray Sweden K Cummins USA G Diendorfer Austria F Heidler Germany A Hussein Canada M Ishii Japan CA Nucci Italy A Piantini Brazil O Pinto Brazil X Qie China F Rachidi Switzerland V Rakov (Convener) USA M Saba Brazil T Shindo Japan W Schulz Austria R Thottappillil Sweden S Visacro Brazil W Zischank (Corresponding Member) Germany
WG Scope
bull Evaluation of current measurements on instrumented towers
bull Evaluation of current measurements for rocket-triggered lightning
bull Evaluation of the procedures used to estimate lightning currents from measured fields with emphasis on those implemented in lightning locating systems
bull Inclusion of additional lightning parameters (eg characteristics of continuing currents return-stroke propagation speed equivalent lightning channel impedance etc) that are presently not on the CIGRE list but needed in engineering applications
bull Further characterization of positive and bipolar lightning discharges
bull Characterization of upward lightning discharges
bull Search for any geographical seasonal and other variations in lightning parameters
bull Preparation of a reference document ldquoLightning Parameters for Engineering Applicationsrdquo based on the current understanding of lightning processes and taking into account limitations of various measuring techniques
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
WG Scope
bull Evaluation of current measurements on instrumented towers
bull Evaluation of current measurements for rocket-triggered lightning
bull Evaluation of the procedures used to estimate lightning currents from measured fields with emphasis on those implemented in lightning locating systems
bull Inclusion of additional lightning parameters (eg characteristics of continuing currents return-stroke propagation speed equivalent lightning channel impedance etc) that are presently not on the CIGRE list but needed in engineering applications
bull Further characterization of positive and bipolar lightning discharges
bull Characterization of upward lightning discharges
bull Search for any geographical seasonal and other variations in lightning parameters
bull Preparation of a reference document ldquoLightning Parameters for Engineering Applicationsrdquo based on the current understanding of lightning processes and taking into account limitations of various measuring techniques
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
24 Ground Flash Density
25 Number of Strokes in a Downward Cloud-to-Ground Flash
27 Multiple Channel Terminations on Ground
31 32 and 35 Lightning Peak Current Distributions
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
9
2 General Characterization of Lightning
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Types of lightning discharges from cumulonimbus
Cloud-to-ground (25) Cloud-to-air
Intracloud Cloud-to- cloud
Cloud discharges (75)
10
Types of Lightning Discharges
10
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Four types of lightning effectively lowering cloud charge to ground Only the initial leader is shown for each type In each lightning-type name given below the sketch the direction of propagation of the leader and the polarity of the cloud charge effectively lowered to ground are indicated
Types of Lightning Discharges CGs
11
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Diagram showing the luminosity of a three-stroke ground flash and the corresponding current at the channel base (a) still-camera image (b) streak-camera image and (c) channel-base current
Downward Negative Lightning Discharges to Ground
12
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Beasley W H and Jordan D M Comparison of High-Speed Video and VHF Source Locations for CG Lightning Flashes AGU 2008 AE24A-02 Photron 10000 frames per second (100 micros frames)
13
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
14
3 Ground Flash Density
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
15
Number of Lightning Strikes to a Structure
When the incidence of only downward lightning strikes is concerned it is common to ascribe the so-called equivalent attractive area to a ground-based object It can be defined as ground-surface area that would receive the same number of strikes as the structure provided that Ng=const For a free-standing structure such as a mast or chimney this area is given by where Ra is the equivalent attractive radius For stretched structures (such as a power line) the equivalent attractive area is termed the shadow zone or attractive swath and expressed as where for power lines L is the line length b is the line effective width and Ra is the equivalent attractive distance thought to be equal to the equivalent attractive radius for a free-standing structure of the same height b is usually taken as the distance between overhead ground wires ( b=0 for a single ground wire)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
16
Number of Lightning Strikes to a Structure
Ra is usually assumed to be a function of structure height h where a and b can be estimated using actual data on lightning incidence to structures of different height as According to the IEEE Std 1243 and the transmission-line flash collection rate Ns (in strikes100 kmyr) is where h and b are in meters and Ng in flasheskm2yr
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
A global map of total lightning flash density (per square kilometer per year) based on data from two satellite detectors Optical Transient Detector (OTD 5 years) and Lightning Imaging Sensor (LIS 3 years) Grey areas 001-01 km-2yr-1 white areas lt001 km-2yr-1
Total Lightning Flash Density ndash Ng(Ng + Nc) is needed
17
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Ground Lightning Flash Density (Ng) ndash 15 years (1997-2011) of observations
18
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
19
Lightning Incidence ndash South Africa
1975-1986 (11 years)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
20
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
21
4 Number of Strokes per Flash
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
22
Number of Strokes per Flash
Location (Reference)
Average Number of Strokes per
Flash
Percentage of Single-Stroke
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
64
13
83
Florida (Rakov and Uman 1990a)
46
17
76
Sweden (Cooray and Perez 1994)
34
18
137
Sri Lanka (Cooray and Jayaratne 1994)
45
21
81
Brazil (Saraiva et al 2010)
39
20
223
Arizona (Saraiva et al 2010)
39
19
209
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
23
5 Multiple Channel Terminations on Grounds
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
24
Multiple Channel Terminations on Ground
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
25
Number of Channel Terminations per Flash
Location (Reference)
Average Number of Channels per
Flash
Percentage of Multigrounded
Flashes
Sample Size
New Mexico (Kitagawa et al 1962)
17 16
49 42
72 83
Florida (Rakov and Uman 1990)
17
50
76
Arizona (Valine and Krider 2002)
14
35
386
France (Berger et al 1996 Hermant 2000)
15
34
2995
Brazil (Saraiva et al 2010)
17
51
138
Arizona (Saraiva et al 2010)
17
48
206
multiple-stroke flashes only including 11 single-stroke flashes assumed to have single channel per flash
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
26
Histogram of the distances between the multiple terminations of 22 individual ground flashes in Florida The distances were determined using optical triangulation and thunder ranging Adapted from Thottappillil et al (1992)
Multiple Channel Terminations on Ground
Min = 03 km Max = 73 km GM = 17 km
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
27
6 Rocket-Triggered Lightning
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
The rocket-and-wire technique for triggering lightning
Schematic illustration of the equipotential surfaces in the lowest 200 m and their interaction with a ldquoclassicalrdquo rocket The equipotentials are closely spaced aloft where the vertical field is assumed to be 50 kVm and near the tip of the rocket where they are concentrated geometrically They are further apart near the ground where the field is greatly reduced by corona space charge
Instrumented triggering facility
wire
28 28
Artificial Initiation (Triggering) of Lightning
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Sequence of Events in Classical Rocket-Triggered Lightning [Rakov 1999]
LeaderReturn Stroke Sequence Initial Stage
29
Artificial Initiation (Triggering) of Lightning
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Rocket-triggered lightning vs natural lightning
Natural
Triggered
Initial Stage (50 ndash 500 A)
~ 5 C
~ 1 C
~ 10 C
~ 1 C
~ 30 C
~ 10 C
~ 1 C
~ 1 C
30
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
31
Fiberglass rocket with a spool of Kevlar-coated copper wire
ICLRT
Wire spool
1-m Rocket
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
32
Photographs of lightning flashes triggered in 1997 at the ICLRT at Camp Blanding Florida Top a distant view of a strike to the test runway bottom a close-up view of a strike to the test power system initiated from the 11-m high tower launcher
ICLRT
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
33
F0321-OFFICE-WIDE
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
34
7 Lightning Peak Current Distributions
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Lightning Parameters
35
Peak current For objects or systems that present an essentially resistive impedance such as under certain conditions a ground rod a power line and a tree the voltage (V) on the object or system with respect to remote ground will be proportional to the current I via Ohms law V = RI where R is the effective resistance at the strike point For example a 10 kA peak current injected into a power line conductor with a 400 Ω characteristic impedance produces a line voltage of 2 MV with respect to the earth
Such a large voltage will cause insulation flashover
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
36
Cumulative statistical distributions of lightning peak currents giving percent of cases exceeding abscissa value from direct measurements in Switzerland (Berger 1972 Berger et al 1975) The distributions are assumed to be lognormal and given for (1) negative first strokes (2) positive first strokes (3) negative and positive first strokes and (4) negative subsequent strokes Adapted from Bazelyan et al (1978)
Lightning peak currents for first strokes vary by a factor of 50 or more from about 5 to 250 kA The probability of occurrence of a given value rapidly increases up to 25 kA or so and then slowly decreases Statistical distributions of this type are often assumed to be lognormal
Lightning Peak Current ndash Bergerrsquos Distributions
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
37
Cumulative statistical distributions of peak currents (percent values on the vertical axis should be subtracted from 100 to obtain the probability to exceed the peak current value on the horizontal axis) for negative first strokes adopted by IEEE and CIGRE Taken from CIGRE Report 63 (1991)
For the CIGRE distribution 98 of peak currents exceed 4 kA 80 exceed 20 kA and 5 exceed 90 kA For the IEEE distribution the ldquoprobability to exceedrdquo values are given by the following equation where ΡI is in per unit and I is in kA This equation applies to values of I up to 200 kA The median (50) peak current value is equal to 31 kA
Peak current I kA (IEEE distribution) 5 10 20 40 60 80 100 200
Percentage exceeding tabulated value ΡI 100
99 95 76 34 15 78 45 08
( ) 62
311
1I
PI+
=
Lightning Peak Current ndash IEEE and CIGRE Distributions
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
38
Brazil Visacro et al (2004 2011) presented a statistical analysis of parameters derived from lightning current measurements on the 60-m Morro do Cachimbo tower near Belo Horizonte Brazil A total of 38 negative downward flashes containing 109 strokes were recorded Median peak currents for first and subsequent strokes were found to be 45 and 18 kA respectively higher than the corresponding values 30 and 12 kA reported for 101 flashes containing 236 strokes by Berger et al (1975) Possible reasons for the discrepancy include 1) a relatively small sample size in Brazil 2) dependence of lightning parameters on geographical location (Brazil versus Switzerland) and 3) different positions of current sensors on the tower at the two locations (bottom of 60-m tower in Brazil versus top of 70-m tower in Switzerland) Visacro and Silveira (2005) using a hybrid electromagnetic (HEM) model and assuming a 100-m long upward connecting leader showed that for typical subsequent-stroke current risetimes peak currents at the top and bottom of the Morro do Cachimbo tower should be essentially the same
Lightning Peak Current ndash Recent Direct Measurements
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Visacro et al Updated statistics of lightning currents measured at Morro do Cachimbo station Atmospheric Research 117 (2012) pp 55ndash63
(1985-1998 amp 2009-2010)
First strokes Median 45 kA
Subs strokes Median 18 kA (16 kA -gt 18 kA)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Lightning Peak Current ndash Recent Direct Measurements
40
Japan Takami and Okabe (2007) presented lightning return-stroke currents directly measured on 60 transmission-line towers (at the top) whose heights ranged from 40 to 140 m A total of 120 current waveforms for negative first strokes were obtained from 1994 to 2004 This is the largest sample size for negative first strokes as of today The median peak current was 29 kA (26 kA after compensation for the 9-kA lower measurement limit) which is similar to that reported by Berger et al (1975)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
41
Measurements in Japan
(a) Schematic diagram of instrumentated tower (b) Photograph of strike rod and Rogowski coil on top of the tower Adapted from Takami et al (2007)
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Comparison of return-stroke peak currents (the largest peak in kA) for first strokes in negative downward lightning
References Location Sample size
Percent exceeding tabulated value σlogI (base
10)
Remarks
95 50 5
Berger et al (1975) Switzerland 101 14 30 (~30) 80 026 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
80 14 31 69 021 Direct measurements on 70-m towers
Dellera et al (1985) Italy 42 - 33 - 025 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa 29 7 33 (43) 162 042 Direct measurements on a 60-m mast
Takami and Okabe (2007)
Japan 120 10 29 85 028 Direct measurements on 40- to 140-m transmission-line towers
Visacro et al (2011) Brazil 38 21 45 94 020 Direct measurements on a 60-m mast
Anderson and Eriksson (1980)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=11) Sweden (N=14)
and USA (N=44)
338 9
30 (34) 101
032 Combined direct and indirect (magnetic link) measurements
CIGRE Report 63 (1991)
Switzerland (N=125) Australia (N=18) Czechoslovakia
(N=123) Poland (N=3) South Africa (N=81) Sweden (N=14)
and USA (N=44)
408 - 31 (33) - 021 Same as Anderson and Erikssonrsquos (1980) sample plus 70 additional measurements from South Africa
The 95 50 and 5 values are determined using the lognormal approximation to the actual data with 50 values in the parentheses being based on the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA As reported by Takami and Okabe (2007) 26 kA and 032 after compensation for the 9-kA lower measurement limit
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
43
Austria Diendorfer et al (2009) analyzed parameters of 457 upward negative flashes initiated from the 100-m Gaisberg tower in 2000ndash2007 Upward flashes contain only strokes that are similar to subsequent strokes in downward flashes ie they do not contain first strokes initiated by downward stepped leaders Some upward flashes contain no strokes at all only the so-called initial-stage current The median return-stroke peak current was 92 kA (n = 615 the largest sample size as of today)
Lightning Peak Current ndash Recent Direct Measurements
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
44
Measurements in Austria
Radio tower at Gaisberg with nearby operational buildings
Top of the Gaisberg tower with air terminal and current-viewing resistor (shunt)
Adapted from Diendorfer et al (2009)
Lightning Peak Current ndash Recent Direct Measurements
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Courtesy of Prof F Rachidi and Prof M Rubinstein
Santis Tower (124 m) Switzerland
Instrumented since May 2010 180 flashes (32 positive) recorded Ng = 2 km-2 yr-1
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
46
Triggered Lightning Schoene et al (2009) presented a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes The flashes were triggered during power-line experiments from 1999 through 2004 at Camp Blanding Florida The return-stroke current was injected into either one of two test power lines or into the earth near a power line via a grounding system of the rocket launcher The geometric mean return-stroke peak current was found to be 12 kA which is consistent with those reported from other triggered-lightning studies
Lightning Peak Current ndash Recent Direct Measurements
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Return-Stroke Current Peak ndash Triggered Lightning
Histogram of return stroke current peaks for 165 strokes in rocket-triggered flashes Camp Blanding Florida 1999 ndash 2004 power line experiments An adjustment factor of 075 has been applied to the current peaks from the 2000 experiment Adapted from Schoene et al (2009)
Direct strikes (n = 144) GM = 12 kA Nearby strikes (n = 21) GM = 11 kA Total (n = 165) GM = 12 kA Direct strikes are to an overhead power line conductor (initial input impedance of about 200 Ω) Nearby strikes are to a 8-m long vertical conductor connected to a concentrated grounding system
47
Lightning Peak Current ndash Recent Direct Measurements
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Comparison of return-stroke peak currents (in kA) for subsequent strokes in negative lightning References Location Sample
size Percent exceeding
tabulated value σlogI Remarks
95 50 5
Berger et al (1975)
Switzerland 135 46 12 30 024 Direct measurements on 70-m towers
Anderson and Eriksson (1980)
Switzerland
114 49 12 29 023 Direct measurements on 70-m towers
Dellera et al (1985)
Italy 33 - 18 - 022 Direct measurements on 40-m towers
Geldenhuys et al (1989)
South Africa
- 7- 8 - - Direct measurements on a 60-m mast
Visacro et al (2011)
Brazil 71 75 18 41 023 Direct measurements on a 60-m mast
Diendorfer et al (2009)
Austria 615 35 92 21 025 Direct measurements on a 100-m tower upward lightning
Schoene et al (2009)
Florida 165 52 12 29 022 Direct measurements triggered lightning
The 95 50 and 5 values are determined using the lognormal approximation to the actual data σlogI is the standard deviation of the logarithm (base 10) of peak current in kA
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Many lightning locating systems such as the US National Lightning Detection Network (NLDN) output a peak current estimate for each stroke using the measured magnetic radiation field peaks and distances to the ground strike point reported by multiple sensors The following field-to-current conversion equation is used
where ip is the peak current in kA and Mean(RNSS) is the mean of rangendashnormalized (to 100 km) signal strengths in so-called LLP units from all sensors allowed by the central analyzer to participate in the peak current estimate This equation implies that the magnetic (as well as electric) radiation field is proportional to the current Normalization of measured signal strength SS to 100 km is performed taking into account signal attenuation due to its propagation over lossy ground The following empirical formula has been used since 2004 to compensate for propagation effects
where r is in kilometers and SS is in LLP units
49
Estimation of Peak Currents from Measured Electromagnetic Fields
minus
=
1000100exp
100rrSSRNSS
( )RNSSMeanip 1850=
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
50
8 Calibration of Lightning Locating Systems
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Camp Blanding
Map showing the locations (as of late 2003) of 15 NLDN sensors in the Florida region Also shown is the location of lightning triggering site labeled ldquoCamp Blandingrdquo The nearest NLDN sensor is located in Ocala at a distance of 89 km Adapted from Jerauld et al (2005)
NLDN Sensors Around Camp Blanding Florida
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Flash and Stroke Detection Efficiencies
Year Number
of Flashes Triggered
Number of NLDN Detected Flashes
NLDN Flash
Detection Efficiency
()
Number of
Strokes
Number of NLDN Detected Strokes
NLDN Stroke
Detection Efficiency
()
2010 12 12 100 51 41 80
2011 11 11 100 38 23 61
2010ndash2011 23 23 100 89 64 72 2004ndash2009 (Nag et al 2011)
37 34 92 139 105 76
2001ndash2003 (Jerauld et al 2005)
37 31 84 159 95 60
In 2010 NLDN misclassified one stroke as a cloud discharge
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Location Errors
Min = 134 m Max = 35 km Median = 436 m
Min = 23 m Max = 42 km Median = 308 m
Min = 40 m Max = 11 km Median = 600 m
Location error is defined as the distance between the location of launcher (used as ground-truth) and the location reported by the NLDN
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
NLDN Peak Current Estimation Error (Absolute)
2010 2011 2010ndash2011
2004ndash2009
2001ndash2003
AM () 15 14 15 17 20 SD () 97 11 10 19 11 Median () 14 16 15 13 20
Min () 16 0 0 0 0 Max () 37 41 41 129 ~ 50 N 33 23 56 96 70
ΔI = INLDN - ICB
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
55
Absolute current estimation errors range from 0 to 50 (Median = 20)
Absolute current estimation errors range from 0 to 129 (Median = 13)
Jerauld et al (2005 JGR) Nag et al (2010)
NLDN Reported Peak Currents vs Those Directly Measured at Camp Blanding Florida (2001-2009)
2001-2003 n = 70
2004-2009 n = 96
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
9 Summary
1 Ground lightning flash density (Ng) is the primary descriptor of lightning incidence Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng
2 About 80 or more of cloud-to-ground lightning flashes are composed of two or more strokes This percentage is appreciably higher than 55 previously estimated by Anderson and Eriksson (1980) based on less accurate records The average number of strokes per flash is typically 3 to 5
3 Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers When only one location per flash is recorded the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 15-17 which is considerably higher than 11 estimated by Anderson and Eriksson (1980)
4 From direct current measurements the median return-stroke peak current is about 30 kA for first strokes in Switzerland Italy South Africa and Japan and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning Corresponding values from measurements in Brazil are 45 kA and 18 kA
5 The field-to-current conversion procedure employed by the NLDN and other similar systems has been calibrated only for negative subsequent strokes with the median absolute error being 10 to 20
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Rocket-Triggered Lightning at Camp Blanding Florida (2009) Photograph by Dustin Hill
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
58 58
Four strokes that were time correlated with power-line faults and the associated 50 confidence regions Originally 24 faults (in 2 years) were suspected to be due to lightning Strokes 1-3 were near 69-kV lines and stroke 4 was near a 230-kV line Adapted from Cummins et al (1998)
Lightning protection studies (Sacramento Municipal Utility District)
Recommended