Observation of preliminary breakdown and leader propagation characteristics in a negative cloud to ground flash with two strike points

Abstract

High-speed video and electric field data were used to analyze a preliminary breakdown process and three different types of leader processes in a negative cloud to ground flash with two strike points. The preliminary leader was multi-branched and significantly brighter than the stepped leader, with the speed varying from 1.4 × 106 m/s to 6.4 × 105 m/s in a decreasing trend. Two types of chaotic leaders were proposed and compared. Type 1 chaotic leaders last for approximately 0.3 ms, with speed greater than 107 m/s, and no change in leader type throughout the whole leader process. Type 2 chaotic leaders with a duration of approximately 0.5 ms and speed on the order of 106 m/s transformed into a dart-stepped leader with a continuously decreasing speed in the leader process, and the pulse amplitude of chaotic leaders tended to decrease during the transition. The attenuation of the pulse amplitude in electric field (E-field) and the insufficient amount of charge may be responsible for such a conversion.