Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge

Abstract

An on‐ground observation program for high energy atmospheric phenomena in winter thunderstorms along Japan Sea has been performed via measurements of gamma‐ray radiation, atmospheric electric field and low‐frequency radio band. On February 11, 2017, the radiation detectors recorded gamma‐ray emission lasting for 75 sec. The gamma‐ray spectrum extended up to 20 MeV and was reproduced by a cutoff power‐law model with a photon index of urn:x-wiley:grl:media:grl57457:grl57457-math-0001, being consistent with a Bremsstrahlung radiation from a thundercloud (as known as a gamma‐ray glow and a thunderstorm ground enhancement). Then the gamma‐ray glow was abruptly terminated with a nearby lightning discharge. The low‐frequency radio monitors, installed ∼50 km away from the gamma‐ray observation site recorded leader development of an intra/inter‐cloud discharge spreading over ∼60 km area with a ∼300 ms duration. The timing of the gamma‐ray termination coincided with the moment when the leader development of the intra/inter‐cloud discharge passed 0.7 km horizontally away from the radiation monitors. The intra/inter‐cloud discharge started ∼15 km 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.