Luminosity with intracloud‐type lightning initial breakdown pulses and terrestrial gamma‐ray flash candidates

Abstract

AbstractHigh‐speed video data for four hybrid lightning flashes show luminosity bursts at visible wavelengths that are time‐correlated with large, intracloud flash (IC) initial breakdown (IB) pulses in electric field change (E‐change) data. The candidate IC‐type IB pulses are large in range‐normalized E‐change amplitude and peak current (2.2‐3.4 V/m at 100 km, 2.9‐11.1 kA) and have slow (0.3‐2.2 ms duration) field changes corresponding to charge moment changes of 0.5‐15 C km. Such large amplitude IB pulses have been associated with production of terrestrial gamma‐ray flashes in prior work. No gamma‐ray observations were available for these events. In each flash, a luminosity increase was evident in the video data at the time of the largest IC‐type IB pulses, when VHF sources and E‐change data indicate the IC initial leader was at 6.1 ‐ 9.4 km altitude and rapidly developing upward. Luminosity starts increasing within ‐10 µs to +20 µs of the main IC‐type IB pulse peak, i.e., within the same 20‐µs video frame as that in which the E‐change peak occurs. Delay time between the beginning of the E‐change pulse and beginning of the luminosity increase is 40‐110 µs. Video intensities increase sharply for 80‐220 µs to maximum value, then decrease over a longer period, with entire burst durations of 300‐800 µs. The time lag between IB pulse peak and maximum luminosity is consistent with these IC‐type IB pulses starting a large current that peaks and becomes bright at the time of the main pulse peak, and lasts for several hundred microseconds.