A comparative study of the electrical characteristics of positive and negative narrow bipolar events

Narrow bipolar events (NBEs) are one sort of intriguing intra-cloud discharges that receive enormous interest in the lightning community. They come with two polarities dominating at different altitudes in thunderclouds. The sources of negative NBEs are usually located near the top of thunderclouds, and positive NBEs are at the middle levels. NBEs may occur at the onset of lightning, but the electrical properties of NBEs remain not well understood. Here, we present the first comparative study on the electrical characteristics of negative and positive NBEs. An improved method based on the transmission line model is applied to derive electrical parameters from the fast electric field change waveforms of 1673 positive NBEs and 364 negative NBEs recorded by the Jianghuai Area Sferic Array (JASA) in China. It is found that negative NBEs occurring at high altitudes tend to produce a narrower current pulse and take a shorter time to traverse the channel than their positive counterparts. Moreover, a larger portion of negative NBEs is associated with slightly greater peak current moment but smaller overall charge moment compared to their positive counterparts. The discrepancies in electrical properties between negative and positive NBEs reported in our work suggest the difference in charge distributions at different altitudes in NBE-producing thunderstorms.