Characteristics of Narrow Bipolar Pulses observed from lightning in Sri Lanka

• Temporal features of Narrow Bipolar events of both polarities were studied.
• The dominant polarity recorded was of the negative type with a percentage of 78.
• Majority of the pulses were very narrow.
• Nearly one third in magnitude when compared to historic studies of both polarity.
• Narrowness is considered to be due to minimal propagation effects on the signal.

A detailed study on electric field characteristics of Narrow Bipolar Pulses (NBP) observed in Sri Lanka is presented here. NBPs analyzed in this work were recorded at a coastal location in the Southern part of Sri Lanka (Matara: 5.95 °N, 8.53 °E), from five highly active consecutive thunderstorm days during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. Both positive and negative NBPs were observed in this study with the negative type being the most frequent. Parameters presented in this study were the rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width of half maximum (FWHM), the pulse duration and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values of negative NBPs for these parameters were found to be 0.58 µs, 3.01 µs, 0.20 µs, 1.38 µs, 19.21 µs and 0.19 respectively. Similarly, for positive events corresponding values were 1.38 µs, 4.66 µs, 0.48 µs, 1.93 µs, 16.42 µs and 0.37 respectively. The above values conforms to a much narrower bipolar events when compared to previously reported values which is considered to be caused by the propagation effects of signals captured by the apparatus.