资源环境科技发展态势分析平台

An on-ground observation program for high-energy atmospheric phenomena in winter thunderstorms along the Japan Sea has been performed via measurements of gamma ray radiation, atmospheric electric field, and low-frequency radio band. On 11 February 2017, the radiation detectors recorded gamma ray emission lasting for 75s, and then abruptly terminated with a nearby lightning discharge. The gamma ray spectrum extended up to 20MeV and was reproduced by a cutoff power law model with a photon index of 1.36-0.04+0.03, being consistent with Bremsstrahlung radiation from a thundercloud (known as a gamma-ray glow or a thunderstorm ground enhancement). The low-frequency radio monitors, installed approximate to 50km away from the gamma ray observation site recorded leader development of an intracloud/intercloud discharge spreading over approximate to 60km area with a approximate to 300-ms duration. The timing of the gamma ray termination coincided with the moment when the leader development of the intracloud/intercloud discharge passed 0.7km horizontally away from the radiation monitors. The intracloud/intercloud discharge started approximate to 15km away from the gamma ray observation site. Therefore, the glow was terminated by the leader development, while it did not trigger the lightning discharge in the present case.

Plain Language Summary This study presents high-energy radiation, atmospheric electric field and low-frequency radio measurements of winter thunderstorms in Japan. Long-duration gamma ray bursts, called gamma ray glows, are thought to originate from electrons accelerated and multiplied by strong electric fields in thunderclouds. There are unsolved questions such as electron-acceleration mechanisms, position of the acceleration site, lifetime, and life cycle of the bursts. We observed a gamma ray burst lasting for approximate to 75s from a thundercloud abruptly terminated with a lightning discharge. The gamma ray source was destroyed by a cloud-to-cloud discharge over the gamma ray observation site but not related to the triggering of the discharge in the present case.