VLF spectral characteristics of leader pulses

VLF spectra radiated by the stepped leaders of lightning discharges have been obtained by a wideband technique, recording the atmospheric waveforms during active thunderstorms using an aperiodic receiver. From the detailed experimental study it is found that the VLF amplitude spectra of a series of leader pulses will be broad when the mean pause time between successive steps of leader pulses is of the same order as its own standard deviation. Further, if the standard deviation is very small compared to the mean pause time of stepping, the spectra would have a number of peaks at the repetition frequency of the stepping and its harmonics. Two types of stepped leader (¿¿ and ¿¿-type) have been distinguished in terms of their spectral shapes.