Estimation of triggered‐lightning dart‐stepped‐leader currents from close multiple‐station dE/dt pulse measurements. Issue 4 (18th February 2015)

• Record Type: Journal Article
• Authors: Gamerota, W. R.; Uman, M. A.; Hill, J. D.; Ngin, T.; Pilkey, J.; Jordan, D. M.
• Is Part Of: Journal of geophysical research. Volume 120:Issue 4(2015:Mar.)
• Page Start: 1458
• Page End: 1475
• Publication Date: 2015-02-18
• Subjects: Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2014JD022815
• Languages: English
• ISSNs: 2169-897X

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>The modified transmission line model is used to derive the vertically propagating leader‐step currents necessary to radiate measured dart‐stepped‐leader d<italic>E</italic>/d<italic>t</italic> pulses from triggered lightning at close range (<400 m) and low altitude (<70 m). The model‐predicted d<italic>E</italic>/d<italic>t</italic> pulses were compared with measured d<italic>E</italic>/d<italic>t</italic> pulses at nine locations ranging from 27 to 391 m from the channel base for four d<italic>E</italic>/d<italic>t</italic> pulses radiated from two triggered dart‐stepped leaders. The d<italic>E</italic>/d<italic>t</italic> pulses at the closest station, 27 m, were unipolar, dominated by electrostatic and induction components of the radiated d<italic>E</italic>/d<italic>t</italic>, and of opposite polarity to the more distant initial d<italic>E</italic>/d<italic>t</italic> peaks. The other, more distant, eight stations exhibited bipolar d<italic>E</italic>/d<italic>t</italic> pulses, being more or less dominated by the d<italic>E</italic>/d<italic>t</italic> 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 d<italic>E</italic>/d<italic>t</italic> 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<sup>8</sup> m/s with exponential spatial current decay constants from 13 to 27 m. One d<italic>E</italic>/d<italic>t</italic> 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.</p> </abstract>