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

摘要

High-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.