Characterization of negative cloud-to-ground lightning in Florida

Abstract

We examined characteristics of negative cloud-to-ground lightning flashes using their electric field waveforms acquired at the Lightning Observatory in Gainesville (LOG), Florida in the summers of 2013 and 2014. Flash multiplicity, interstroke interval, flash duration, and first to subsequent stroke field peak ratio are determined for 478 flashes containing 2188 strokes and compared with previous results obtained in Florida and in other regions. We found that the average number of strokes per flash is 4.6 and the percentage of single-stroke flash is 12%. The geometric means of interstroke interval, flash duration, and first to subsequent stroke field peak ratio are 52ms, 223ms, and 2.4, respectively. About one-third (34%) of multiple-stroke flashes have at least one subsequent stroke whose field peak is greater than that of the first stroke. The geometric mean of normalized electric field peak shows a relatively weak tendency to decrease with increasing stroke order. We also found that the detectability of preliminary breakdown (PB) pulse train is affected by the signal/noise ratio, type of storm, peak current and distance. For 222 PB pulse trains, statistics on pulse duration, time interval between PB pulse train and return stroke (PB–RS interval), and PB–RS field peak ratio (PB/RS ratio) are presented. Very short PB–RS (≤6ms) intervals were observed to be associated with very high return-stroke peak currents and stepped-leader speeds.