Atmospherics from lightning flashes with multiple strokes

Abstract

The atmospherics resulting from the individual return strokes of a multiple lightning discharge to earth are considered. Special attention is paid to the differences between the source spectra for first and subsequent strokes. It is shown that the change in the velocity of ascent of the return stroke, between a first and a following stroke, implies a shift of the spectrum toward the low-frequency end. On the other hand, the more rapid current rise associated with subsequent strokes entails an intensification of the higher frequencies. A combination of these effects suggests that the source spectrum is effectively constant for all strokes at frequencies exceeding 10 kc/s, and that the main differences occur below this frequency. A straightforward experimental method of checking these conclusions is outlined.