Dynamics of branching of negative downward lightning leaders

Abstract

The branching of negative downward lightning leaders is of both theoretical insterest and practical importance. In the lightning protection of ground structures, a clearer understanding of the mechanism and dynamics of leader branching is needed to identify possible lightning strike locations as well as vulnerable parts of the protection systems. In this work, we start with the image analysis of a lightning leader process recorded with a high-speed camera and to show that the anode-directed streamer zone developed from space stems in front of a leader tip needs be smaller in size (<10 m) to make branching more likely to occur. Then, we propose a kinetic model to describe the growth of the meter-scale streamer zone, which essentially states that the growth speed decreases as the streamer zone expands. The exponent in the kinetic model can be estimated by comparing the numerical and observational results. Based on the model, the streamer zone dynamics on the meter-scale differs from that of a single streamer in that the slowing down of the growth is accompanied by the recovery of the electric field at the discharge front, which may result in new bursts of streamers. This model, if further verified, could be the foundation of inferring the structure and dynamics of the streamer zone from the morphology of the leader channel, which would significantly advance the knowledge of the streamer zone in negative lightning leaders.