XXXVI. The waveforms of atmospherics

Abstract

A convenient and economical technique for recording the waveforms of atmospherics is described, a time resolution of 3 microseconds being achieved with a photograph of total duration, 20 milliseconds. The character of the main waveform types observed at Cambridge has been examined with particular reference to the effects of the distance and direction of the originating lightning discharges. At night, the type of waveform observed depends upon the geographical location of the source; for storms to the south-west, a transition in waveform type occurs at a distance of about 1600 km; no similar change is observed for sources in a south-easterly direction. A critical discussion is given of the applicability of the theory of multiple ionospheric reflections to the various types of waveform, and of the accuracy with which the effective height of reflection and the distance of the source can be determined. Only a small proportion of atmospherics recorded, rarely more than 10% on any one night, yield precise values of these quantities; the height of reflection is found to be about 85 km. The smooth regular oscillatory type, originating beyond 1 600 km to the south-west, cannot be explained by a straightforward application of the reflection theory.