Lightning discharge process based on short-baseline lightning VHF radiation source locating system

Abstract

A lightning VHF radiation source location system based on short-baseline technology is used to study the location of VHF radiation source in the lightning discharge process. The observation was conducted in Daxing'anling during summer of 2009. Positive cloud-to-ground (CG) lightning, negative CG lightning, and intra-cloud (IC) lightning are analyzed based on the locating results and simultaneous electric field changes. The long lasting preliminary breakdown process of CG flash appears as two-level structure of discharge channel in cloud. There are obvious recoil streamers during the final stage of preliminary breakdown process. The preliminary breakdown process propagates at a speed of about 104 m/s. The preliminary breakdown seems to be necessary for the initiation of stepped leader. The stepped leader starts from the source region of preliminary breakdown and propagates downwards. The stepped leader produces intensive VHF radiation. The propagation speed of stepped leader is about 105 m/s. The K process is caused by the streamers propagating backwards and forwards along the electrified channel. Characteristics of discharge processes before and after the return stroke of positive CG flash are different from those of negative CG flash obviously. During long continuing current after the return stroke of positive CG flash, discharges in cloud produce intensive VHF radiation. The energy spectrum of the VHF radiation produced by lightning is studied statistically. It is found that the energy spectrum of VHF radiation decreases quickly with the frequency at a rate of about f-2.9 between 125 and 200 MHz.