On the interpeak interval of unipolar pulses of current preceding the return stroke in negative CG lightning

摘要

Features of the pre-return stroke phase of negative CG lightning are discussed with respect to their unipolar pulses of current induced along grounded structures. Discussions are based on two videos and simultaneous records of current and electric field of flashes obtained at Morro do Cachimbo Station. Traditionally, these pulses induced by the steps of the negative leader approaching the ground are used for revealing propagation characteristics of this leader. It is shown that different branches of the downward leader are responsible for inducing specific sequences of pulses. A procedure was applied for distinguishing such sequences in a significant number of measured lightning currents and their interpeak intervals were estimated from records of current of 18 flashes and 20 unconnected leaders. These intervals were found to be mostly in the 30-50 mu s range, with an average of about 40 mu s. This result is significantly different from that published in literature, derived from electric field records, that reports interpeak intervals ranging from 1 to 100 mu s and an average of about 10-20 mu s.