Waveforms of first and subsequent leaders in negative lightning flashes

Abstract

Statistics on the occurrence of different categories of leader electric field wave shapes are presented as a function of stroke order and distance for 286 strokes in 73 flashes. Electric field records of 71 first strokes and 182 subsequent strokes in 74 flashes are analyzed for leader duration. At distances closer than 5 km, 92% of 38 leader waveforms are hook‐shaped with a net negative field change regardless of stroke order (1 through 18). For strokes of order 8 through 13, 90% of 49 leader waveforms are hook‐shaped with a net negative field change regardless of distance (3 through 14 km). Sixteen percent of 270 subsequent leaders exhibited a marked inactive final portion characterized by a flattening in their field waveforms, the overwhelming majority (84%) of these leaders being associated with early strokes in a flash (2 through 4). In 77% of cases in which this electric field flattening was observed, the leaders were preceded by strokes creating a new termination on ground. The geometric mean leader duration for 71 first strokes was found to be 35 ms, while that mean for 154 subsequent strokes following the same channel as the preceding stroke was 1.8 ms. Twenty‐eight subsequent strokes creating a new termination on ground showed a geometric mean leader duration of 15 ms. The geometric mean leader duration for strokes following the same channel as the preceding stroke exhibited a tendency to increase with stroke order.