Estimation of triggered‐lightning dart‐stepped‐leader currents from close multiple‐station dE/dt pulse measurements

Abstract

The modified transmission line model is used to derive the vertically propagating leader-step currents necessary to radiate measured dart-stepped-leader dE/dt pulses from triggered lightning at close range (<400 m) and low altitude (<70 m). The model-predicted dE/dt pulses were compared with measured dE/dt pulses at nine locations ranging from 27 to 391 m from the channel base for four dE/dt pulses radiated from two triggered dart-stepped leaders. The dE/dt pulses at the closest station, 27 m, were unipolar, dominated by electrostatic and induction components of the radiated dE/dt, and of opposite polarity to the more distant initial dE/dt peaks. The other, more distant, eight stations exhibited bipolar dE/dt pulses, being more or less dominated by the dE/dt radiation component. The derived leader-step current has a slow front that precedes a fast transition to peak amplitude followed by a slow decay to zero after several microseconds. For the four modeled dE/dt pulses, the estimated causative leader-step current peak amplitudes varied from 0.9 to 1.8 kA, the half-peak widths ranged from 370 to 560 ns, the charge transfers were about 1 mC, and the peak current derivatives were about 10 kA/μs. The upward propagation speeds of the leader-step current were from 1.1 to 1.5 × 10 8 m/s with exponential spatial current decay constants from 13 to 27 m. One dE/dt pulse is analyzed in more detail by studying changes in model-predicted waveforms versus current initiation altitude and by examining the effect of varying model input parameters.

A unified engineering model of the first stroke in downward negative lightning

“…[] and Gamerota et al . [] modeled individual leader steps and compared model‐predicted electric field and electric field derivative waveforms to those observed at ground at distances of a few to several hundred meters. Hill et al .…”

“…Stepped and dart leader models are reviewed in Rakov and Uman [2003, chapter 12]. Howard et al [2011] and Gamerota et al [2015] modeled individual leader steps and compared modelpredicted electric field and electric field derivative waveforms to those observed at ground at distances of a few to several hundred meters. Hill et al [2011] and Campos et al [2014] studied characteristics of stepped leaders using high-speed video observations.…”