Analysis on Characteristics of Sub-microsecond Electric Field Change Waveform during the Initial Stage of Lightning Discharge

The characteristics of sub-microsecond electric field change waveforms during the initial stage of intracloud (IC) flashes and preliminary breakdown process of cloud-to-ground (CG) flashes have been studied based on the observation data. The data include fast electric field change and slow electric field change of IC flashes and CG flashes measured in Yangbajing of the Tibetan Plateau in 2008, and in Da Hinggan Ling in 2009. It is found that the electric field change waveforms during the initial stage of IC flashes and preliminary breakdown process of CG flashes appear as a series of pulses. The majority of pulses are narrow with pulse width less than or equal to 10 μs. The majority of pulses are weak with the normalized amplitude value less than 0.5. Compared with the lower altitude area, the number of pulses during the preliminary breakdown process of negative CG flashes measured in the Tibetan Plateau is larger and the proportion of narrow pulses is smaller. The proportion of large bipolar pulses with large peak-to-peak amplitude that is equal to or larger than the peak amplitude of electric field change of the first return stroke is small. Based on the statistics, the mechanism of discharge processes that produce bipolar pulses has been discussed theoretically. It is found that if the propagation speed of current pulse and the damp length of current pulse are large, the peak-to-peak amplitude of bipolar pulse will be large.