Total Lightning Signatures of Thunderstorm Intensity over North Texas. Part I: Supercells

摘要: It is shown that total lightning mapping, along with radar and National Lightning Detection Network (NLDN) cloud-to-ground lightning data, can be used to diagnose the severity of a thunderstorm. Analysis of supercells, some of which were tornadic, on 13 October 2001 over Dallas–Fort Worth, Texas, shows that Lightning Detection and Ranging (LDAR II) lightning source heights (quartile, median, and 95th percentile heights) increased as the storms intensified. Most of the total (cloud to ground and intracloud) lightning occurred where reflectivity cores extended upward, within regions of strong reflectivity gradient rather than in reflectivity cores. A total lightning hole was associated with an intense, nontornadic supercell on 6 April 2003. None of the supercells on 13 October 2001 exhibited a lightning hole. During tornadogenesis, the radar and LDAR II data indicated updraft weakening. The height of the 30-dBZ radar top began to descend approximately 10 min (2 volume scans) before tornado touchdown in one storm. Total lightning and cloud-to-ground flash rates decreased by up to a factor of 5 to a minimum during an F2 tornado touchdown associated with this storm. LDAR II source heights all showed descent by 2–4 km during a 25-min period prior to and during this tornado touchdown. This drastic trend of decreasing source heights prior to and during tornado touchdown was observed in two storms, but did not occur in nontornadic supercells, suggesting that these parameters can be useful to forecasters. These observations agree with tornadogenesis theory that as the updraft weakens, the mesocyclone can divide (into an updraft and downdraft) and become tornadic.