Characteristics of Cloud-to-Ground Lightning Associated with Violent Tornadoes

Abstract

Cloud-to-ground (CG) lightning patterns were analyzed in 42 violent tornado-producing (F4, F5) supercells that occurred between January 1989 and November 1992. The purpose of this analysis was to identify potential correlations between CG lightning patterns and tornadogenesis. Lightning characteristics were analyzed for a 30-min period before, during, and 30 min after each tornado?s lifetime. Thirty-one of the storms were characterized by a peak in CG flash rate preceding tornado formation; 20 storms displayed a decrease in CG flash activity coincident with tornado touchdown. Six of the 42 storms exhibited a polarity reversal, from positive to negative, in the sign of the charge lowered to ground. Storms exhibiting a majority of positive flashes were generally associated with long-track tornadoes, F5 damage ratings, or severe weather outbreak conditions. The total number of flashes associated with each storm had no correlation with tornadogenesis (total number of flashes ranged from 16 to 3394). Based on this analysis, it appears that using CG lightning flash patterns exclusively to detect tornado formation is not practical. The amplitudes of the flash rate changes are too variable to be used as a prognostic tool. The flash rate trends do, however, suggest a recurring relationship to tornado formation. Therefore when used in conjunction with other operational tools, CG flash rate analysis may provide additional information useful in identifying changes in thunderstorm intensity.