Presentation on theme: "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."— Presentation transcript:
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
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