On the characteristics of some radiation fields from lightning and their possible origin in positive ground flashes

Abstract

Characteristics of some radiation field waveforms of lightning from thunderstorms Sweden are presented. The waveforms are distinctly different from previously published signatures from intracloud discharges. In general, they are similar to the radiation fields produced by return strokes in negative ground flashes except for the initial polarity, but several important differences are found in the detailed characteristics. The zero‐to‐peak rise times of these waveforms are found to be in the range 5–25 μs. The waveforms begin with an initial portion or front which rises slowly for 3–20 μs to about half of the field peak amplitude. The observed mean values of 13 μs and 9 μs of zero‐to‐peak rise time and front duration, respectively, of these waveforms are about twice the corresponding values observed for negative return strokes. The mean radiation field peak value, normalized to 100 km, for these waveforms is 2 times that for negative return strokes. Some waveforms were preceded by small‐amplitude pulses which are assumed to be produced by a leader process. The mean separation in time of these pulses is about 26 μs, which may be compared with 14 μs observed for negative return strokes. Another important feature is the presence of ‘slow tails’ in some of these waveforms, indicating the presence of long‐lasting currents in their sources. It is suggested that the sources of the observed waveforms are return strokes bringing down positive charge to earth.