1:45 PM - 3:15 PM
[MIS24-P04] Gamma ray and radio wave analysis of five consecutive TGFs observed in Kanazawa, Japan on December 30, 2021
Keywords:Lightning Gamma Ray, Lightning, Radio Wave, High Energy Atmospheric Physics, Atmospheric Electricity
Lightning is a familiar phenomenon, but there are many unanswered questions. Lightning gamma rays are bremsstrahlung emission from relativistic electrons accelerated up to ~30 MeV in thunderclouds. The phenomena can be separated into two types; Terrestrial Gamma-ray Flash (TGF), which is emitted at a moment of less than ms associated with lightning discharges, and Gamma-ray Glow, in which the thundercloud itself emits gamma rays for several minutes. The high-energy electrons are believed to be accelerated by the electrostatic field in thunderclouds and amplified by avalanche, a phenomena called RREA, but the location of its acceleration site, as well as its required conditions are not known yet. We are participating in the GROWTH (Gamma-Ray Observation of Winter Thunderclouds) experiment to investigate the location of the electron acceleration zone . In FY2021, we deployed two large collimator detectors GOOSE (Gamma-ray Orientation Observing System with Electron-monitor) and several medium-sized scintillator detector MaGaMo (Main Gamma-ray Monitor) in several locations in Kanazawa City.
On December 30, 2021, at around 04:08:34(JST), TGF was detected by two GOOSE detectors installed at the Ishikawa Prefectural Police Academy and Ishikawa Children's Activity Center, and three medium-size detectors installed at Ishikawa Prefectural Izumigaoka High School, Kanazawa University High School, and Kanazawa University. At the time of detection, the area where these five gamma-ray detectors were located had 5-20 mm of precipitation per hour, and gamma-ray glow was observed approximately 3 km northwest of these gamma-ray detectors (Tsurumi et al. JpGU 2022 talk). Radio signal of lightning discharge was observed using FALMA (Fast Antenna Lightning Mapping Array) and DALMA (Discone Antenna Lightning Mapping Array) deployed by Gifu University. Data analysis of five gamma-ray detectors showed that five consecutive TGFs occurred between 04:08:34.868 and 04:08:34.873. Although individual gamma-ray detectors were partially saturated, the beginning and end of individual TGFs were measured. The second, third and fourth TGFs had durations of about 100 µs, while the first and fifth had durations of about 400 and 200 µs, respectively. Furthermore, comparison of the gamma-ray and radio data revealed the presence of slow discharge radio pulses at the same time as the onset of theTGF 1 to 4 (and possibly also TGF 5). The location of these 4 slow pulses are calculated to be above the five gamma-ray detectors, which were separated from the main discharge activity located ~4 km to the north.
On December 30, 2021, at around 04:08:34(JST), TGF was detected by two GOOSE detectors installed at the Ishikawa Prefectural Police Academy and Ishikawa Children's Activity Center, and three medium-size detectors installed at Ishikawa Prefectural Izumigaoka High School, Kanazawa University High School, and Kanazawa University. At the time of detection, the area where these five gamma-ray detectors were located had 5-20 mm of precipitation per hour, and gamma-ray glow was observed approximately 3 km northwest of these gamma-ray detectors (Tsurumi et al. JpGU 2022 talk). Radio signal of lightning discharge was observed using FALMA (Fast Antenna Lightning Mapping Array) and DALMA (Discone Antenna Lightning Mapping Array) deployed by Gifu University. Data analysis of five gamma-ray detectors showed that five consecutive TGFs occurred between 04:08:34.868 and 04:08:34.873. Although individual gamma-ray detectors were partially saturated, the beginning and end of individual TGFs were measured. The second, third and fourth TGFs had durations of about 100 µs, while the first and fifth had durations of about 400 and 200 µs, respectively. Furthermore, comparison of the gamma-ray and radio data revealed the presence of slow discharge radio pulses at the same time as the onset of theTGF 1 to 4 (and possibly also TGF 5). The location of these 4 slow pulses are calculated to be above the five gamma-ray detectors, which were separated from the main discharge activity located ~4 km to the north.