Characteristics of Impulsive Currents Superimposing on Continuous/Continuing Current of Rocket-Triggered Lightning

Characteristics and mechanism of initial continuous current (ICC) pulses and M components in rocket-triggered lightning were investigated in detailed. The geometric mean current peak, risetime from 10% to 90% peak, half-peak width, and charge transfer of M components were 400 A, 207 μs, 267 μs, and 0.19 C, respectively, exhibiting more pronounced impulsive feature than ICC pulses of which the counterpart parameters were 190 A, 462 μs, 845 μs, and 0.27 C, respectively. A shorter time interval between the prior return stroke (RS) and the following M component (TRS-M) facilitated a stronger M component having larger peak while shorter pulsewidth. In two cases with extremely long lasting ICC and continuing current (CC), 20 Initial continuous current pulses occurred during a 715.3-ms duration and 15 M components occurred during a 218-ms duration. The multiple occurrences of current surges serve to keep the grounding channel active and extend the channel network inside the cloud, and hence prolong the ICC/CC duration. This situation reduced the possibility of RSs thereafter. In addition to the two traditional types of in-cloud discharges that result in M component, we recognized a new scenario that involves a short-term interruption of the upward RS wave and a reactivated breakdown promoted by the residual charge inside the main channel.