A class of unusual lightning electric field waveforms with very strong high‐frequency radiation

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Abstract
The first wideband dE/dt recordings have been obtained for the narrow bipolar pulses previously identified by Le Vine (1980) as “sources of the strongest RF radiation from lightning.” These dE/dt waveforms are dramatically different from those of other known lightning processes. A burst of high‐frequency “noise” is superimposed on the slower bipolar pattern one might expect from the relatively smooth E waveforms. For 18 such pulses from an isolated thunderstorm cell at known range, the mean peak E and dE/dt, range‐normalized to 100 km, were 8.0±5.3 V/m and 20±15 V/m/μs, respectively. Spectral analysis indicates that the sources of these pulses radiate much more strongly than first‐return strokes at frequencies from 10 MHz to at least 50 MHz. Absolutely calibrated power and energy spectra are presented which are reliable from 200 KHz to perhaps 20 MHz. At 18 MHz the narrow pulses appear to contain nearly 16 dB more spectral energy than first return‐stroke waveforms from the same range. Supporting evidence shows that they generally occur as isolated pulses in intracloud flashes but are not associated with K changes or other known phenomena. They can occur in either polarity.