Simultaneous observations of electric field changes, wideband magnetic field pulses, and VHF emissions associated with K processes in lightning discharges

摘要

We studied simultaneous electric field changes, microsecond-scale (VLF/LF) magnetic field pulses, and VHF emissions associated with K processes in 37 cloud and 54 cloud-to-ground lightning flashes that occurred in a local convective thunderstorm in Shanghai. All the observed features were very similar for both types of flashes. Over 98 of the 1252 observed K changes were associated with detectable microsecond-scale pulses, although only about 26 of them were accompanied by large pulses whose amplitude exceeds by at least 50 the average amplitude of the five largest pulses in the flash. VHF bursts, which almost always coincide in time with microsecond-scale pulses, can occur either during K changes or during the gaps between K changes. About 9 of K changes were observed to be associated with regular pulse trains, with pulses in the train showing one-to-one correspondence to VHF bursts and occurring at a geometric mean interval of 6.9 μs. Overall, our results indicate that small microsecond-scale pulses are an inherent feature of K processes. We infer that the K process can be viewed as a fast negative leader, but only those leaders with appreciable charge transfer show step/ramp-like K changes in electric field records.