Meteorological Aspects of Gamma‐Ray Glows in Winter Thunderstorms

Abstract

During three winter seasons from November 2016 to March 2019, 11 gamma‐ray glows were detected at a single observation site of our ground‐based gamma‐ray monitoring network in Kanazawa, Japan. These events are analyzed with observations of an X‐band radar network, a ceilometer, a disdrometer, and a weather monitor. All the detected glows were connected to convective high‐reflectivity regions of more than 35 dBZ, developed up to an altitude of >2 km. They were also accompanied by heavy precipitation of graupels. Therefore, graupels in the lower layer of thunderclouds that correspond to high‐reflectivity regions can form strong electric fields producing gamma‐ray glows. Also, these events are compared with a limited sample of nondetection cases, but no significant differences in meteorological conditions were found between detection and nondetection cases in the present study.

Structure of thunderstorm ground enhancements

“…It is widely accepted, that the cloud charge structure for a typical thunderstorm contains an upper positive charge region consisting of ice crystals, a main negative charge region consisting of both graupel and ice crystals, and a lower positive charge region consisting of graupel (Kuettener, 1950). The electric charge of graupel is positive at temperatures warmer than -10° C, and negative at temperatures cooler than -10° C (Takahashi, 1978, Wada et al, 2021. In review (Williams, 1989) was stated that the tripolar structure of thunderstorms is supported by a wide variety of observations and that temperature appears to be the most important single parameter in controlling the polarity of charge acquired by the precipitation particles.…”

Catalog of Gamma-ray Glows during Four Winter Seasons in Japan

“…The variations in the number of events by observation sites are shown in Figure 8. As mentioned in Wada et al [21], the largest number of gamma-ray glows were detected at site 5, Kanazawa University Kakuma Campus; 15 events for four years. The lower panel shows the normalized distribution by operational days.…”

“…Among the 70 gamma-ray glows, 66 glows have a significance of more than 5σ, and the remaining 4 glows have less significance. Nineteen events have been reported in our previous publications [21][22][23][24]. There are simultaneous detections with nearby detectors (events 2 and 3 for example).…”

Atmospheric Electron Spatial Range Extended by Thundercloud Electric Field Below the Relativistic Runaway Electron Avalanche Threshold

“…We assume a cloud region with a quasi‐constant and homogeneous electric field to provide the electron accelerations and produce secondary gamma ray photons. Winter thunderstorms along the Sea of Japan, as gamma ray glow emitters, are thought to have a tripolar charge structure (Williams, 1989) as reported in the literature (Takahashi, 1978; Wada et al., 2021). Here we assume that the electric field region is formed between the negative charge and lower positive charge centers and thus electrons are accelerated downward.…”

“…(1994) discovered Terrestrial Gamma ray Flashes (TGFs), which are microsecond‐lasting enhanced gamma ray bursts with energy reaching tens of MeV related with lightning discharges (Briggs et al., 2010; Smith et al., 2005; Tavani et al., 2011). A wide variaty of observations of other High Energy Atmospheric Phenomena (HEAP) (Babich, 2003) demonstrate interactions between the thundercloud electric field and high‐energy particles; including gamma ray glow (also called Thunderstorm Ground Enhancement, TGE and long bursts; Chilingarian, 2013; Wada et al., 2021), neutron bursts (Babich, 2019; Babich et al., 2007; Chilingarian, Bostanjyan, Karapetyan, & Vanyan, 2012; Chilingarian, Bostanjyan, & Vanyan, 2012; Martin & Alves, 2010; Shah et al., 1985; Shyam & Kaushik, 1999;) and TGFs afterglow (Diniz et al., 2018, 2021; Enoto et al., 2017; Rutjes & Ebert, 2017).…”