Forecasting Lightning Initiation and Cessation at Kennedy Space Center

Henry FuelbergFlorida State University

• Each year lightning strikes U.S. ~ 25 million times• Plus 3 to 50 times as many cloud flashes• Positive vs. Negative Flashes • Voltage = 100 million V • Amperage = 5,000 - ~250,000 A• Temperatures reaching ~50,000oC • ~ 80 people killed each year in U.S.• ~ 300 injuries each year in U.S.• ~26,500 house fires annually due to lightning• Total insurance claims ~ $ 1 Billion• Total costs ~ $ 5-6 Billion

U.S. Lightning Factoids

Non-Inductive Charging Mechanism• Charging occurs when ice crystals and graupel collide in the

presence of supercooled water (mixed phase region of storm).

• Updrafts carry lighter particles with positive charge aloft.• Heavier particles with negative charge sink to bottom of storm.

Krebiehl (1986)

Cloud-to-Ground Lightning

High Speed Photography

• Marcello Saba—INPE, Sao Paulo, Brazil 7000 frames per second

Up Close

Positive Flashes

• Deposit positive charge on surface• Usually a single stroke• Often strike away from storm core, up to 5-10

miles away• Longer continuing current• Stronger peak current• Therefore….more dangerous

Positive Flash Scenario• Often initiates in the upper (anvil) region of storms• After most of the heaviest precipitation has fallen from a cell, the

upper positive charge is exposed to the ground.

Classical Thunderstorm• While

Satellite-Based Lightning Detection• Optical detectors on polar satellites• GOES-R to be launched in 2015

Ground-Based Lightning Detection

National Lightning Detection Network

National Lightning Detection Network

• Data from 1989-Present

U.S. Lightning Distribution from NLDN

Florida Leads the Nation • Warm season (June-Aug)• Many heavily populated

areas are vulnerable.• Enhanced flash densities are

due to: -- Sea breezes and

lake/river breezes -- Shape/orientation of

the coastline.

Flashes/ km2/ warm season

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Lightning Detection and Ranging (LDAR) Network

■ Detects VHF “sources”, or stepped-leaders of IC and CG flashes

■ Limited detection of sources near the ground (CG flashes)

■ Sources combined into flashes using spatial and temporal constraints

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Initiation and Cessation

■ Typically, cloud-to-ground (CG) lightning is second-leading cause of weather-related fatalities in the U.S. behind flash floods

■ Most casualties occur either before or after the most intense lightning activity.

■ Forecasting the first and last flash of a storm is very important

Leon the Lightning Safety Lion

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Forecasting the First Flash■ Can you see the storm approaching?■ Many studies have related radar parameters to first flash■ Wolf [2006] studied over 1000 single cell, multicell, and

supercell storms in the southern U.S.

■ Pretty good at forecasting lightning initiation■ Is inverting lightning initiation criteria useful for forecasting

total lightning cessation?

Charging is sufficient for CG flashes to occur

CG lightning initiation follows

Sufficient hydrometeors in the mixed-phase region

of the cloud

Ascent of 40 dBZ echo above

-10°C

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Purpose of FSU Study■ Safety is critical at Kennedy Space Center■ 25,000 persons, $25 billion of facilities■ U.S. Air Force’s 45 Weather Squadron

issues lightning advisories.■ Many operations must be suspended

while lightning is a threat.

(From Weems et al., 2001)

(From Rudlosky)

Forecasting the Last Flash

• Little is known about cessation• 45WS maintains warnings too long• Wasted man power• Improved forecasts could produce a cost

savings of $millions per year• But…safety is the primary concern

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Warning Decision Support System – Integrated Information (WDSS-II) + LDAR

■ Allows you to merge and manipulate radar + LDAR data

■ LDAR source density grids (2 km horizontal and 1 km vertical resolution)

■ WSR-88D quality-controlled and gridded at ~1 km resolution.

■ Radar data ingested as it arrived in each elevation scan

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Storm Cell Tracking■ Using WDSS-II clustering and tracking algorithm:

■ Identify storms based on a selected parameter■ Set clustering thresholds low enough to track storm cores through cessation■ Data mine each cluster■ 120 statistics are computed within each cluster to produce time-series

VIL Density field with 4 associated storm clusters on 1 Sep 2005

Clustering small, isolated, weakening cells = major challenge! Maximum values are used, as in prior studies

Assess Temporal Relations

• Describe lightning variability using radar characteristics

• Describe the variability in radar parameters using lightning data

0

2

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19.0

419

.1419

.2319

.3219

.4019

.4919

.5819

.6719

.7619

.8419

.9320

.0220

.1120

.2220

.3120

.4620

.5520

.64

Time (UTC)

Hei

gh

t (k

m)

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1.2

Fla

shes

km

-2 s

ec-1

Top18 Top30 Top50 Average CG Maximum CG

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19.0

419

.1419

.2319

.3219

.4019

.4919

.5819

.6719

.7619

.8419

.9320

.0220

.1120

.2220

.3120

.4620

.5520

.64

Time (UTC)

Hei

gh

t (k

m)

0

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So

urc

es k

m-2

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-1

Top18 Top30 Top50 Average VILMA Maximum VILMA

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Total IC Flashes = 14581

Total CG Flashes = 2238

Hei

ght A

GL

(km

)H

eigh

t AG

L (k

m)

IC Flashes

CG Flashes

Normalized Time [0.0 = Time of first flash, 1.0 = Time of last flash]

Normalized Time [0.0 = Time of first flash, 1.0 = Time of last flash]

Time-Normalized Initiation Heights

Time-Normalized Initiation Heights

Do Frequency/Altitude HoldAnswer ?

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Do Peak Currents Hold Answer?

Normalized Time [0.0 = Time of first flash, 1.0 = Time of last flash]

Peak

Cur

rent

(kA)

Time-Normalized CG Flash Peak Currents for 116 storms

Total CG Strikes = 2524

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Do Multiplicities Hold Answer?

Normalized Time [0.0 = Time of first flash, 1.0 = Time of last flash]

Mul

tiplic

ity

Time-Normalized CG Flash Multiplicities for 116 storms

Total CG Strikes = 2524

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■ Figure 18 is the time-height plot of several parameters for a typical single cell on 17 May 2002. The WDSS-II cluster-derived radar and LDAR source density data encompass the duration of lightning activity, from before the first flash at 1940:47 UTC until after the last flash at 2044:57 UTC. Greatest source densities occur at ~1956 UTC, ~33% through the storm’s duration. Thus, greatest source densities in the storm’s core occur near the middle of its life cycle when reflectivities greater than 40 dBZ extend higher than 7 km (the height of the -10°C isotherm). Most IC flashes initiate above the freezing level (0°C), while CG flashes originate at lower altitudes, generally below the height of the -10°C isotherm. The lapse rate of reflectivity at t = 0.5 (halfway through storm duration) is 4.05 dBZ km-1, increasing to 5.85 dBZ km-1 at cessation. The reflectivity contours remain at a relatively constant height during most of the storm’s lifetime, but descend during the last several minutes. The 40 dBZ echo descends below the height of -10°C by the time of the last lightning flash, an IC flash at 2044:57 UTC.

Gradual or Abrupt Decay

• Figure 19 illustrates a single cell storm that occurred on 13 August 2000. WDSS-II cluster statistics begin ~2 min after lightning initiation. One should note the absence of lightning activity between 2049 and 2107 UTC. While no lightning occurs during this 18 min period, a final IC flash does occur at 2107:29 UTC. This is one of the 6 storms in the original 116 storm dataset that experiences an “outlier”-type of decay [Stano et al., 2009], with an apparent cessation at ~2047 UTC and one last “surprise” IC flash at 2107:29 UTC. IC flash initiations again are located above the 0°C isotherm (Figure 18); however, a comparison of reflectivity profiles (Figures 18 and 19) shows that the altitudes of flash initiations and source density contours are more dispersed in the current storm (Figure 19). The greatest source density again occurs at ~2027 UTC, about 33% through the storm’s duration. One should note that the height of -20°C is 9 km (1 km higher than in the previous case). The lapse rate of reflectivity is 4.80 dBZ km-1 at t = 0.5, increasing to 6.39 dBZ km-1 at the last flash. Contours of reflectivity exceeding 35 dBZ are at a nearly constant altitude below -10°C throughout the last 40% of the storm duration, from ~2046 to 2107 UTC, with downward sloping occurring only after the last flash. There is no clear indication that this storm will experience an “outlier” cessation behavior; however, reflectivity contours near the end of its lifecycle are more constant in altitude than the other two cases in this section. We hypothesize that the nearly constant reflectivity contours below -10°C indicate a small rate of electrification. Charge may build up gradually in the storm until the breakdown threshold is finally met, resulting in the final IC flash.

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“outlier”

20 min

Outliers

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Lightning Bubbles

Numerous Statistical Approaches Tried1. Forward Stepwise Regression

-- Sounding only parameters-- Storm (lightning +radar) and sounding

parameters2. Event Time Trends

-- Storm duration vs. Maximum interval 3. Lag Time of Radar Values to Cessation

-- Compare time from maximum height of maximum DBZ to time of

cessation4. Percentile Method ***

-- Break maximum interval values into percentiles

Most Successful – Percentile Method

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Max Int50th75th95th99.5

Max

imum

Inte

rval

(min

)

Maximum Interval Percentiles 116 storms

1. Most Successful-- Superior accuracy-- Performed well with

boot-strap method-- Only method successful with “outliers”

2. Smaller Time Savings-- ~5 minute savings-- Accuracy from extended

wait times-- Limited by “outliers”-- However, provides

certainty to advisories

Provisional KSC Cessation Rule1. Provisional Rule

-- Decaying storm with no expected redevelopment

-- Consider cancellation at 15 min-- If redevelopment possible

OR-- Attached anvil cloud

-- Extend advisory up to 25 min and continue to observe

before cancellation2. Potential Time Savings

-- Current advisories maintained ~20-25 minutes

-- As Provisional Rule gains confidence may decrease to 15-20 min

-- ~22% time savings-- Significant monetary savings over

year

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Current Research■ Looking more closely at anvil region■ Looking more closely at outliers (common features ?)■ Include dual polarimetric radar in research

■ Explore hydrometeor profiles prior to cessation.

We Can’t Stop Lightning, But…

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Acknowledgements

■ Holly Anderson Melvin M.S.■ Geoffrey Stano Ph.D.■ Funding Sources

Thank You for Inviting Me !!

Go Buckeyes—As long as your are not playing FSU

Lightning vs. Wind Direction Wind from East Warm Season Wind from West