Abstract
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.
Highlights
Two types of high-energy events have been detected from thunderstorms
terrestrial gamma-ray flashes” (TGFs) and gamma-ray glows are distinguished clearly by duration, brightness, and timing with regard to lightning discharges, both of them are thought to originate from a common fundamental mechanism, called relativistic runaway electron avalanches (RREAs39,40)
Bi4Ge3O12 (BGO) scintillation crystal coupled with two photomultiplier tubes (PMTs; HAMAMATSU R1924A)
Summary
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. Downward TGFs that contains enough photons above 10 MeV have been experimentally shown to trigger atmospheric photonuclear reactions, namely producing neutrons and positronemitting radioactive nuclei[13,14] These photoneutrons can be observed as a short-duration gamma-ray burst lasting for several hundreds of milliseconds, as they are absorbed by atmospheric nuclei via neutron-capture processes[14,18]. Gamma-ray glows, referred to as long bursts[19] or thunderstorm ground enhancements[20], are energetic radiation from thunderclouds with energies up to tens of MeVs, lasting for a few seconds to several minutes They have been observed by airborne detectors[1,21,22,23], at mountain-top[20,24,25,26,27,28,29] and sea-level observation sites[19,30,31,32,33]. We report the first unequivocal simultaneous detection of them at sea level and discuss its implications
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