Electric field signatures of narrow negative bipolar pulse activities from lightning observed in Sri Lanka

Isolated Narrow Bipolar Pulses (NBP) have been observed in the past in sub tropical and tropical regions. This study presents detail electric field characteristics of NBP pulses observed in Sri Lanka in the tropic. NBP analyzed in this work were recorded at Matara (5.95 °N, 8.53 °E), southern coast of Sri Lanka from four highly active thunderstorm days in May 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. In contrary to previous observations at the same geographical region, both positive and negative NBP pulses were observed in this study. Parameters related to Narrow Negative Bipolar Pulses (NNBP) are presented in this study since majority of the observations were in that category. The parameters measured for NNBP´s were rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width at half maximum (FWHM) and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values for these parameters were found to be 0.49 μs, 2.83 μs, 0.18 μs, 1.18 μs and 0.17 respectively. The above values conforms to a much narrower bipolar pulses when compared to values reported in earlier studies.