Electrical characteristics of narrow bipolar events

Abstract

Narrow bipolar events (NBE) are the electromagnetic signature of a distinct class of impulsive and energetic intra‐cloud discharge that occurs in some thunderstorms. NBE are characterized by strong VHF RF emissions and bipolar waveforms when observed by broadband field‐change antennas at large distances. These discharges may occur in isolation or precede and perhaps initiate conventional intra‐cloud flashes. When observed at close range, NBE waveforms exhibit electrostatic field changes in addition to the bipolar radiation field change. At extremely close range, the induction and electrostatic fields dominate in our measurements. Using close‐range observations in conjunction with the radiation‐field measurements, I calculate that on average, an NBE transfers 0.3 C of charge over a distance of 3.2 km and that the discharge wave front propagates at a speed equal to one‐half the speed of light.