Characteristics of narrow bipolar Events

From analysis of data collected by a 6-station local network, we report observations of 1395 positive narrow bipolar events (NBEs) and 144 negative NBEs occurring in the mid-low latitude Jianghuai area in China. The source height of each NBE was derived from the ionospheric reflections followed the narrow bipolar waveform. Positive NBEs occurred at a mean altitude of 9.7 km, much lower than 16.0 km for negative NBEs. However we also found that about 4% of positive NBEs occurred at the same altitudes as negative NBEs. On a statistical basis, negative NBEs, which tended to occur at higher heights than positive NBEs, were different from positive NBEs in time waveform features as well as electric field strength. However, negative NBEs showed the similar time waveform features to those positive NBEs which originated at same altitudes as negative NBEs. Characteristics of current which was thought to produce narrow bipolar pulses, in terms of peak current moment and peak charge moment, were also derived from observed narrow bipolar electric field waveforms. A NBE discharge involved in the peak current moment as much as 30 kA-km, while the charge transferred can be of the order of 0.4-0.5 C.