Signatures of electric field pulses generated by cloud flashes

Electric field signatures of cloud flashes belonging to Swedish thunderstorms have been analysed for different parameters within the first 10 ms of the flashes. The waveforms were recorded with a 10 ns resolution. Pulses with both polarities were analysed and many of them were found to begin with slow fronts followed by fast transitions. The magnitudes of the peak amplitude, the amplitude of overshoots, the rise time (10-90% of the peak), the full-width at half-maximum (FWHM), the zero crossing time, the time interval between consecutive pulses, the amplitudes of slow fronts and ratio of the peak amplitude to the amplitude of overshoot were analysed. The average values of these parameters were found to be 1.46, 0.59 V/m, 0.64, 0.68, 1.96, 35.7μs, 0.84 V/m, and 3.54, respectively. Investigations were made to find possible correlations between different pulse signatures. Out of the total number of 238 pulses (both polarities) from 12 cloud flashes, the amplitude of the overshoot shows a linear relationship with the peak amplitude whereas no such relation could be seen between the peak amplitude and any other parameter. However, linear correlations were shown by the rise time with the FWHM, the rise time with the zero crossing time and the FWHM with the zero crossing time. Similar relations were observed when the pulses were investigated for individual polarity, except for the peak amplitude and amplitude of overshoot of negative pulses, which do not show a linear relationship. Slow fronts were analysed only for the positive pulses, being dominant in the cloud flashes under this study, and 101 pulses were selected from 12 flashes with slow fronts. The amplitudes of these slow fronts were found to be varying up to 60% of the corresponding peak amplitude. The time interval between the consecutive pulses was found to be varying from 0.38 to 500μs.