Gamma-ray glow preceding downward terrestrial gamma-ray flash

Two types of high-energy events have been detected from thunderstorms. One is “terrestrial gamma-ray flashes” (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting “gamma-ray glows”. Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for ~100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within ~1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF. Thunderstorms are thought to produce two types of high-energy emissions, terrestrial gamma-ray flashes and gamma-ray glows however due to the difficulty in their observation the exact relation between the two is still not well-understood. Here, the authors report the simultaneous detection of a gamma-ray glow and a downward terrestrial gamma-ray flash suggesting the origin of the two phenomena are related.