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

Narrow bipolar events (NBEs) are intriguing intra-cloud discharge that have attracted enormous interest in the lightning community. They come with two polarities that dominate at different altitudes in thunderclouds. The sources of negative NBEs are usually located near the top of thunderclouds; those of positive NBEs are at the middle levels. NBEs may occur at the onset of lightning. The electrical properties of NBEs remain poorly understood. We present here the first comparative study of the electrical characteristics of negative and positive NBEs. 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, we use an improved method based on the transmission line model. This approach concludes 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, compared to positive NBEs, a larger portion of negative NBEs are associated with slightly greater peak current moments but smaller overall charge moments. The differences reported herein between electrical properties of negative and positive NBEs suggest that charge distribution in NBE-producing thunderstorms tends to vary systematically with altitude.