On the field‐to‐current conversion factors for large bipolar lightning discharge events in winter thunderstorms in Japan

Abstract

AbstractIn this paper we have simulated the far‐field waveform characteristic of large bipolar events (LBEs) occurred in winter thunderstorms in Japan and compared the field‐to‐current conversion factors (FCCFs) of LBEs with that of the lightning cloud‐to‐ground (CG) return stroke (RS) in summer thunderstorm. As for the physical process of LBEs, Wu et al. (2014) considered that LBEs may be very similar to the typical lightning RS (RS‐like process) or caused by an initial continuous current pulse (ICC‐like process) in upward lightning flashes. We assume that the lightning channel length of LBEs ranges from 500 m to 1000 m, and the height of tall object struck by LBEs is from 100 m to 300 m. By using the bouncing wave model, we found that only when the injected current waveform of LBEs is characterized with a symmetric Gaussian pulse, the simulated far‐field waveform of LBEs both for RS‐like process and ICC‐like process is similar to that observed by Wu et al. (2014). For striking tall objects with heights from 100 m and 300 m, the FCCFs of LBEs are positively correlated with its channel length and derivatives of injected current waveform, and the FCCF for RS‐like process is about similar to that for ICC‐like process. However, the FCCFs of LBEs are very different from lightning RS in summer thunderstorm; that is to say, the FCCFs developed for the well‐known lightning RS in summer thunderstorm are not suitable for LBEs.