Development characteristics of triggered lightning with fast initial continuous current pulses and two grounding points

In this paper we analyze the current, electromagnetic field and optical data of a rocket-triggered lightning with two grounding points. There are 4 fast initial continuous current pulses (ICCPs) in the initial stage. Fast ICCPs have larger amplitudes and shorter rise times than those of typical ICCPs, which are mostly found in tower-initiated upward lightning. The formation of fast ICCPs are not only related to the height of the junction point, but also to the value of the initial continuous current (ICC) in the main discharge channel to ground. For the same height of the junction point, the lower the value of ICC, the more likely it is to produce fast ICCP. The lightning has three return strokes (RS1-RS3). The new grounding point forms after RS2. The location and time of the new grounding point formed is different from the previously reported “anomalous” triggered lightning and is closer to the natural lightning. The two-dimensional distance between the grounding points was 543 m. The formation of new grounding point may be associated with large leader deviation angle and low intracloud charge. The occurrence of RS3 was preceded by multiple attempted leaders (ALs). Based on the analysis of the source charge leader model, the “slow-fast-slow” trend of the electric field waveform in leader stage before RS3 might be related to the speed change of leader.