EXPLORING THE USE OF A PHYSICALLY BASED LIGHTNING CESSATION NOWCASTING TOOL E. V. Schultz 1, W. A. Petersen 2, L. D. Carey 1 1 Univ. of Alabama in Huntsville and 2 NASA/Wallops Flight Facility 35 th Conference on Radar Meteorology, Pittsburgh, PA 26 – 30 September 2011

 Funding from the NASA Space Shuttle Program and Terrestrial Environments Office at MSFC  45 th Weather Squadron at Cape Canaveral Air Force Station  Geoffrey Stano for current work with the VAHIRR algorithm.

 $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

 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

 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

 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?

 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

Z (km) KDP (°/km) +- Charging Layer Strong Electric 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. Weak Electric field Electric field dominates Aerodynamic forces dominates

 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.

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

 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)

 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

2259 UTC 3×3 VAHIRR11×11 VAHIRR Courtesy G. Stano

2322 UTC 3×3 VAHIRR11×11 VAHIRR Courtesy G. Stano Time of cessation

2342 UTC 3×3 VAHIRR11×11 VAHIRR Courtesy G. Stano

KDP PHIDP

Last flash occurred at 2322 UTC 14 minutes after last flash31 minutes after last flash Charging layer

3 minutes before 4 minutes after 20 minutes after 37 minutes after

Z (km) KDP (°/km) +- Charging Layer -5°C -40°C As 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.

 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