Radar and Atmospheric Sounding observations around 23 TGFs

Abstract:

This study employs 23 Terrestrial Gamma-ray Flashes (TGF) detected with NASA’s Fermi Gamma-ray Burst Monitor (GBM) and collocated with the World Wide Lightning Location Network and the Earth Networks Total Lightning Network with 9 WSR-88D (NEXRAD) located in Brownsville and Corpus Christy (Texas), Lake Charles (Louisiana), Key West, Miami, Tampa and Eglin Air Force Base (Florida), San Juan (Puerto Rico) and Andersen Air Force Base (Guam). The NEXRAD Enhanced Echo Tops (EET) and Vertical Integrated Liquid Density (VILD) are traditional proxies to storm height and severity. To retrieve the storm characteristics we construct probability histograms of respective EET and VILD values around each TGF.Here we show that although high-topped storms are consistently present in the vicinity of TGFs, the VILD values indicate storms of disparate convective strengths. In particular, the majority of our TGF sample is encompassed by storms of high EET (>10-11 km) values and in their majority overall VILD < ~2.0 gr m^-3.These EET and VILD values are common in summertime oceanic/coastal low-latitude thunderstorms where the main convective core is limited in the first few kilometres and the updrafts are weak and narrow. Qualitative observations from the temporal evolution of the volumetric radar reflectivity shows that in a few cases the TGF emission signals the dissipation stage of the main convective core, although this suggestion is tentative and requires more sophisticated and currently ongoing storm tracking techniques. The atmospheric soundings (where available in spatial and temporal proximity with the respective TGF) indicate that TGF producing storms can exhibit a significant variation in their respective thermodynamic environment and type (e.g. regular to high CAPE, pulse vs. high shear etc). The authors acknowledge the valuable contributions of the GBM Team, Bob Holtzworth (WWLLN) and Stan Heckman (ENTLN).