Characteristics of Port Moresby ground flashes

Abstract

An investigation into the characteristic features of lightning flashes to ground in Port Moresby, Papua New Guinea (latitude 9°S, longitude 147°E), has been carried out. A scheme is presented for the identification of discharge features from simultaneous records of optical radiation, electric field change, and HF radiation. Data were obtained from records of 80 identified ground flashes comprising 282 strokes, 202 interstroke intervals, 223 continuing currents, and 53 stepped leaders. Flash durations are log normally distributed with a geometrical mean of 604 ms and a standard deviation of 0.25 decade. Sixty‐eight per cent of pre‐first‐stroke processes had durations exceeding 100 ms, the mean being 240 ms. Of 59 flashes outside the reversal distance electric field, records of 80% indicated that negative charge was raised before the first return stroke. The distribution of stepped leader durations is normal with a mean of 21 ms and standard deviation of 8 ms. Interstroke intervals are approximately log normally distributed, with a geometrical mean of 61 ms and a standard deviation of 0.36 decade. The geometrical mean value of continuing current duration is 5.5 ms and the standard deviation 0.70 decade, but the distribution is neither normal nor log normal. Of 34 multiple stroke flashes, 47% have at least one long continuing current. The form of the frequency distribution of continuing current duration may reflect a fundamental distinction between long and short continuing currents: however, it is probably the result of differences between the 1976 and 1977 distributions.