The relation between the number of strokes,stroke intervals and the total durations of lightning discharges

Summary Although lightning flashes have been photographed which apparently have up to 40 or more component strokes, no flashes having more than 14 strokes have been observed on records of the eletrical fields of thunderstorms. The apparent discrepancy between the two methods of observation is explained by the fact that small momentary increases in the continuing current flowing to ground after some strokes, are easily mistaken for component strokes on photographs taken with slow cameras.After the cessation of a discharge, the ionization of the lightning channel decreases at such a rate that a subsequent discharge to earth will require a fresh leader if it follows within an interval longer than about 15 millisec; discharges following at shorter intervals are not preceded by leaders. The channel loses its ionization completely in about 100 millisec.In general, the larger the number of component strokes, the longer is the duration of the flash, but there is no definite relationship between the number of strokes and the duration.Flashes of exceptionally long duration always have one or more very long intervals between two successive strokes and during these intervals there appears to be very little electrical activity in the cloud; it is suggested that the main progress of the discharge in the cloud takes place during the shorter intervals, so that flashes of long duration do not necessarily drain very extensive regions of charge.I wish to thank the South African Council for Scientific and Industrial Research for a grant in aid of this research.