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 similar to 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 similar to 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.