[M-IS19] Atmospheric electricity and application of technology for reducing disaster risks

[MIS19-08] Citizen Science “Thundercloud Project” observation report for the winter of 2024

*Miwa Tsurumi¹, Teruaki Enoto^1,2, Yuko Ikkatai³, Naoki Tsuji¹, Ting Wu⁴, Daohong WANG⁴, Taro Shinoda⁵, Kazuhiro Nakazawa⁵, Jun Kataoka⁶, Diniz Sousa Gabriel⁷, Masashi Kamogawa⁸, Toru Takagaki⁹, Shoko Miyake¹⁰, Takeshi Morimoto¹¹, Yoshitaka Nakamura¹², Harufumi Tsuchiya¹³ (1.Kyoto University, 2.RIKEN, 3.Kanazawa University, 4.Gifu University, 5.Nagoya University, 6.Waseda University, 7.National Institute of Space Research, 8.University of Shizuoka, 9.TAC, 10.Gifu National College of Technology, 11.Kindai University, 12.Kobe City College of Technology, 13.JAEA)

Keywords:gamma-ray glow, citizen science, mapping radiation observation

In a developed thunderstorm cloud, electrons are accelerated to relativistic speeds by a strong electric field, emitting bremsstrahlung in the gamma-ray band. This phenomenon is called “gamma-ray glow,” and gamma rays in the MeV range have been observed on the ground for tens of seconds to a minute upon the passage of a thunderstorm cloud. Since gamma rays in the atmosphere decay within a few hundred meters, it is necessary to observe clouds at low altitudes. Ground-based observations of gamma-ray glow phenomena have been actively conducted on the Sea of Japan side in winter because low-level clouds are generated when cold, dry air from the Siberian air mass passes through the warm Tsushima Current. This previous study revealed that electrons are accelerated by the electric field in thunderclouds and emit gamma rays, and that this electric field region is generated by charged particles such as ice crystals and graupel in thunderclouds. However, the limited number of observation points makes it difficult to track moving thunderclouds, which hinders the measurement of the temporal and spatial distribution of the gamma-ray emission region. To solve these problems, the “Thundercloud Project” was launched using a citizen science framework. With the help of citizen supporters in the Hokuriku region, lightweight and compact radiation detectors called “Cogamo” were installed around the city of Kanazawa in winter. Combining these detectors with automatic data transmission by Sakura IoT, a large-scale observation network was constructed. By increasing the scale and density of the observation network at multiple locations, we aim to track thundercloud and unravel the mysteries of thundercloud gamma-ray radiation, including the onset, continuation, and termination of electron acceleration within cumulonimbus clouds. It also aims to identify thunderclouds in which electron acceleration occurs and to determine whether accelerated electrons trigger lightning discharges.
In FY2024, 70 Cogamo detectors are installed throughout Ishikawa Prefecture, mainly in Kanazawa City, and observations are conducted from November to March. In addition, new detectors capable of detecting charged particles and neutrons as well as gamma rays have been installed since the end of January.
At least 50 events have been observed so far this fiscal year. On November 29, when lightning activity was particularly active, a total of 22 events were detected. On December 17 and November 28, events were detected at Kanazawa University, where an electric field meter was installed. In this presentation, we will report the results of the comprehensive analysis of gamma-ray data, electric field meter data, and XRAIN data.