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

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.