Synoptic meteorological conditions of gamma-ray glows in winter thunderstorms

The Gamma-ray Observation of Winter Thunderclouds collaboration has detected 70 gamma-ray glows, a high-energy phenomenon associated with thunderstorms, from October 2016 to March 2020 in Kanazawa and Komatsu, Ishikawa Prefecture, a central part of Japan facing the Sea of Japan. Based on surface and 500 hPa analyses, numerical prediction models, and surface and satellite observations, we classify their synoptic meteorological conditions into mainly three types. Most of the glow-detection cases were in west or west-southwest winds around the detection sites. Over half of the cases took place when a convex structure of surface pressure, often associated with a trough at 500 hPa, was formed along the coast of the Sea of Japan. Besides, we extract non-detection cases during winter thunderstorms in Kanazawa to compare with the glow-detection cases. While some of the non-detection cases have similar meteorological conditions as the glow-detection cases, most of the non-detection cases exhibited higher temperatures at the surface and 850 hPa, and higher - 10 C-? altitudes, which indicates that electrification occurs at higher altitudes than the glow-detection cases. Therefore, gamma rays might have been produced but were attenu-ated before reaching the ground and undetectable at sea level.