  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
$1.36^{+0.03}_{-0.04}$, 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 $\sim$50 km
away from the gamma-ray observation site recorded leader development of an
intra/inter-cloud discharge spreading over $\sim$60 km area with a $\sim$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 $\sim$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.

Atmospheric and Oceanic Physics;High Energy Physics - Experiment