EXPLORING THE USE OF A PHYSICALLY BASED LIGHTNING CESSATION NOWCASTING TOOL

E. V. Schultz1, W. A. Petersen2, L. D. Carey1

1Univ. of Alabama in Huntsville and 2NASA/Wallops Flight Facility

35th Conference on Radar Meteorology, Pittsburgh, PA

26 – 30 September 2011

ACKNOWLEDGEMENTS

Funding from the NASA Space Shuttle Program and Terrestrial Environments Office at MSFC

45th Weather Squadron at Cape Canaveral Air Force Station

Geoffrey Stano for current work with the VAHIRR algorithm.

MOTIVATION FOR A LIGHTNING CESSATION TOOL

$5 Billion insured industry losses/year (NLSI 2008)

Even more in time/manpower loss Many industries are affected by

thunderstorms NASA/KSC, CCAFS, etc. Airports

Recreation Any outdoor activity – everyone is affected

PRIMARY RESEARCH QUESTIONS

To what extent can ice-crystal alignment signatures be used to nowcast the cessation of lightning activity in a given storm?

Does polarimetric data provide significant improvement over current reflectivity and statistical methods in nowcasting lightning cessation?

Past statistical, conventional, and polarimetric radar studies

PREVIOUS WORK

OBSERVATIONS: LIGHTNING STUDIES

Statistically based study at KSC (Stano et al. 2010) 116 storms (32 days in May-Sept) in range of KSC

LDAR system Only tested for warm season in Florida Tested 5 statistical and empirical methods

Percentile method provided best results Results provide 45WS (starting summer 2008) with

objective guidance to safely end advisories Only based on statistics not on physical

characteristics – leaves room for improvement

OBSERVATIONS: RADAR REFLECTIVITY Radar reflectivity and electric field mill data (Bateman et al.

2005) Developed algorithm now known as VAHIRR (volume averaged

height integrated radar reflectivity) Data from ABFM, WSR-74C (Patrick AFB) and WSR-88D (Melbourne)

Serves as proxy for the electric field in non-convective clouds to evaluates the anvil cloud LLCC (Lightning Launch Commit Criteria)

VAHIRR currently in use at KSC – more on this in methodology NEXRAD and NLDN (Wolf, 2006)

Probabilistic guidance for CG alerts using 40 dBZ and -10°C level Relates lightning initiation radar parameters to cessation

applications

Both studies limited to traditional radar reflectivity, can polarimetric radar provide further useful information?

OBSERVATIONS: POLARIMETRIC RADAR Many studies have investigated polarimetric variables

temporal comparison to lightning flashes (e.g., Hendry and McCormick 1976, 1979; Hendry and Antar 1982; Krehbiel et al. 1991, 1992, 1993,1996; Metcalf 1992, 1993, 1995; Caylor and Chandrasekar 1996; Scott et al. 2001; Marshall et al. 2009)

These studies found strong indications of ice crystal orientation using polarimetric radar in thunderstorms Both circular and linear polarizations, simultaneous and

alternating transmissions were investigated over the last 40 years.

PHIDP, KDP, ZDR, and RHOHV have all been shown to have some change before/after a lightning flash.

LDR and CDR have also shown capabilities but are not available for this study using ARMOR

CONCEPTUAL MODEL: ICE CRYSTAL ORIENTATION

Z (km)

KDP (°/km)+-

Charging Layer

StrongElectric field

Ice crystals

-5°C

-40°C

Vertically oriented ice crystals in a strong

vertical electric field.

Horizontally oriented ice crystals in a weak

vertical electric field.

WeakElectric field

Electric field dominates Aerodynami

c forces dominates

DATA AND METHODOLOGY

DATA

Advanced Radar for Meteorological and Operational Research (ARMOR) Dual-polarimetric C-band

radar North Alabama Lightning

Mapping Array (NALMA) Three-dimensional

lightning mapping

Similar set up to the 45WS new dual-Polarimetric radar and KSC LDAR.

DATASET

50+ cases within 100 km of ARMOR Varying temporal resolution PPI or RHIs Different storm types (airmass, multicell,

supercell, linear)

METHODOLOGY

Collect events – previous and future events Investigate temporal and spatial radar resolution

needed within the charging layer for successful use of algorithm

LMA data run through a flash clustering algorithm (McCaul et al, 2005)

Subjective analysis of PHIDP to identify phase shift relationship (infer ice orientation) to last lightning flash within a storm

Smoother (than typical applied) KDP calculation Compare to VAHIRR Particle identification algorithm (PID)

THE VAHIRR PRODUCT

Volume Average Height Integrated Radar Reflectivity Determine horizontal radius of influence

Originally 5 km, giving an 11x11 km area Vertical component extends from cloud base to cloud top

Cloud base: 0°C isotherm or lowest reflectivity, whichever higher Cloud top: Level of 0 dBZ reflectivity

VAHIRR = (volume average reflectivity) × (average cloud thickness)

Advantages Incorporates depth of cloud and reflectivity intensity

information Can detect anvils acting as “capacitors”

Thick anvils with high reflectivity

Courtesy G. Stano

PRELIMINARY RESULTS - 9 SEPT 2009

9 SEPT 2009 – 5KM RADAR REFLECTIVITY

VAHIRR EXAMPLE (09 SEPT 2009)

2259 UTC

3×3 VAHIRR

11×11 VAHIRR

Courtesy G. Stano

VAHIRR EXAMPLE (09 SEPT 2009)

2322 UTC

3×3 VAHIRR

11×11 VAHIRR

Courtesy G. Stano

Time of cessation

VAHIRR EXAMPLE (09 SEPT 2009)

2342 UTC

3×3 VAHIRR

11×11 VAHIRR

Courtesy G. Stano

KDP/PHIDP EXAMPLE

KDP PHIDP

DISTRIBUTION OF KDP WITH HEIGHT

Last flash occurred at 2322 UTC

14 minutes after last flash 31 minutes after last flash

Charging layer

TIME-SERIES OF MEAN KDP WITH HEIGHT

3 minutes before4 minutes after20 minutes after37 minutes after

CHANGES IN KDP RELEVANT TO CESSATION

Z (km)

KDP (°/km)

+-

Charging

Layer-5°C

-40°CAs the electric

field increases, KDP decreases in the charging layer, and the

potential exists for lightning.

After a lightning flash, the

electric field relaxes. Thus, KDP increases

within the charging layer.

The electric field begins to rebuild after a lightning flash

and KDP decreases.

The electric field begins to weaken (increasing KDP)

although no lightning has

occurred. The electric field no longer supports the potential for

lightning.

SUMMARY

A handful of case studies support the KDP lightning cessation model

Additional cases and analysis are necessary to determine time between cessation and end of KDP signature.

More analysis is needed to determine if polarimetric radar will add significant benefit to the current radar reflectivity (VAHIRR) type methods for lightning cessation nowcasting

NEXT STEPS

johnson@nsstc.uah.edu

QUESTIONS?