Evidence of negative leaders prior to fast rise ICC pulses of upward lightning

Abstract

Six initial continuing current (ICC) pulses contained in upward negative lightning were studied. We classified these ICC pulses into two types according to current pulse shapes.The type 1 ICC pulses had a short geometric mean (GM) of 10-90% risetimes of 8.9 μs, while the type 2 ICC pulses had a long GM of 10-90% risetimes of 55 μs. We found that the type 1 ICC pulses had preceding negative leaders which were connected to the channel of the existing ICC. These negative leaders caused the current increases of the ICC pulses by creating the conducting channels. The height of the space charges transferred by the fast rise ICC pulse is estimated to be about 700 m above sea level at most.