Characteristics of the radiation fields from lightning in Sri Lanka in the tropics

Abstract

Characteristics of the radiation fields from (1) stepped leader, (2) return strokes, and (3) cloud flashes in the tropics are presented. The separation between the successive leader pulses immediately preceding the return strokes are distributed over the range of 4–40 μs with a mean value of 12 μs. The ratio of the amplitude of the last leader pulse to that of the return stroke is log‐normally distributed with mean and standard deviation of 0.1 and 0.03, respectively. A correlation between the amplitude of the last leader pulse and the return stroke radiation field peak is observed. Consequences of this correlation are interpreted using the transmission line return stroke model. The initial peak of the return stroke radiation field is followed by several subsequent peaks. The time intervals between the successive peaks and their amplitudes are studied and compared with those observed in Florida. The zero crossing time of the first stroke radiation fields are distributed over the range of 40–160 μs, with a mean and standard deviation of 95 μs and 30 μs, respectively. The corresponding values for the subsequent strokes are 15–75 μs, 42 μs, and 14 μs, respectively. The separation between the subsequent strokes are distributed log normally with a mean and standard deviation of 91 ms and 62 ms, respectively. The average number of strokes per flash is 3.2. Characteristics of a particular type of radiation field pulses from cloud flashes are presented. Initial polarity of these pulses is opposite to that of the return strokes. The amplitudes of these pulses are about 0.2–0.5 of the return stroke amplitudes. Total duration of these pulses is about 70 μs, with initial half‐cycle duration of about 10 μs.