A High Peak Current, Negative Polarity Lightning Process Possibly Associated with TGFs

Abstract:

We report here a distinct class of high peak current lightning processe,. Our analysis approach identifies events of interest using lightning network data and classifies them based on distinct characteristics their full low frequency (LF) and very low frequency (VLF) radio waveforms. Previously we have shown that, in addition to cloud-to-ground (CG) lightning strokes and narrow bipolar events (NBEs), there exist high peak current (>100 kA) events that we termed energetic in-cloud pulses (EIPs) occur during negative leader propagation through high background electric field regions.

This final class of high peak current lightning event is referred to as a large bipolar event (LBE), in acknowledgment that a small number of seemingly similar events have been reported during coastal winter thunderstorms in Japan. The LF waveform characteristics of LBEs are clearly distinct from negative cloud-to-ground lightning, EIPs, and narrow bipolar events (NBEs). Interestingly, LBEs are only observed with negative polarity and are thus either upward-moving positive charge or downward-moving negative charge. They occur close to ground level, unlike the relatively high altitude EIPs. And more interestingly, –LBEs appear to be generated in the US only over mountainous areas with ground elevations above 1500 m.

We conjecture that –LBEs are associated with propagating upward positive leaders that initiated from high points in the terrain. The high peak current and high amplitude radiated fields from these events indicate that they almost certainly produce elves. We also speculate that –LBEs may be associated with downward terrestrial gamma-ray flashes (TGFs), as the production scenario of an upward, ground-attached positive leader in a high electric field produced by the low thunderstorm and terrain is known to sometimes produce TGFs. The geographic distribution of these LBEs thus suggests interesting locations to search for low altitude downward TGFs.