11:00 AM - 1:00 PM
[MIS27-P05] Observation and analysis of thundercloud gamma-ray glows in fiscal year 2021 by the Citizen Science "Thundercloud Project”
Electrons are accelerated to relativistic energy by a strong electric field in developed thunderclouds and lightning. The accelerated electrons collide with the atmosphere and emit bremsstrahlung. The thundercloud gamma-ray glow is a minute-lasting high-energy phenomenon observed at passages of thunderstorms. The energy spectrum of gamma-ray glows extends up to 10 MeV, and their observed duration ranges from seconds to tens of minutes.
The GROWTH experiment, which was launched in 2006, deploys radiation detectors in the Hokuriku region in winter, where gamma-ray glows are frequently detected (e.g., Wada et al., Phys. Rev. Research, 2021). Despite accumulating evidence for electron acceleration due to the electric field in the clouds and lightning discharges, there are several unsolved questions, such as temporal evolution of this phenomena: the birth, growth, disappearance, and duration of thundercloud gamma rays, as well as the size of the electron acceleration region in the cloud.
To solve these questions, we need increased number of observation points to track moving thunderclouds, and started the Citizen science based multipoint observation campaign "Thundercloud Project.". With the cooperation of citizen supporters in this project, a small and portable radiation monitor, called "Cogamo (Compact Gamma-ray Monitor)", are deployed in Kanazawa City, Ishikawa Prefecture during the winter season, making a large-scale observation network. A Cogamo detector have a 5×5×15 cm CsI(Tl) scintillator coupled with a Hamamatsu Photonics MPPC photodetector, and can remotely monitor radiation data along with GPS signals and environmental sensor information. By increasing the area and density covered by this multi-point observation, we will be able to track thunderclouds and elucidate the mysteries of thunderclouds and gamma rays, such as (1) when electron acceleration in thunderclouds starts, how long it lasts, and how it ends, (2) in what types of thunderclouds electron acceleration occurs, and (3) whether accelerated electrons can trigger lightning discharges.
In fiscal year 2021, we have established an observation system of 50 Cogamo detectors in Ishikawa Prefecture and are performed observations from December to March. During this period, we have achieved remote real-time monitoring of gamma-ray glows using an automatic alert system. We also broadcast YouTube movie of a visible camera installed at the Tokyu Hotel in Kanazawa to capture thunderstorms above Cogamo detectors. Here we report the observation and analysis results for the year 2021.
As an example, two Cogamo detectors detected thundercloud gamma-ray glows along a moving cloud over eastern Kanazawa City at 14:20 JST on December 19, 2021. About 160 seconds after one Cogamo detectors detected an increase of about 400 gamma-ray photons, another Cogamo detector about 2 km away from the first one also recorded an event with about 140 photons. Comparing the data with the synthetic rainfall data from XRAIN published by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), this gamma-ray glow event is revealed to be coincided with the movement of the developing rain clouds. We also succeeded in capturing the same gamma-ray emitting cloud with the visible light camera. The camera shows moving clouds with low cloud base altitude, which is important information for understanding the characteristics of the gamma-ray glow.
The GROWTH experiment, which was launched in 2006, deploys radiation detectors in the Hokuriku region in winter, where gamma-ray glows are frequently detected (e.g., Wada et al., Phys. Rev. Research, 2021). Despite accumulating evidence for electron acceleration due to the electric field in the clouds and lightning discharges, there are several unsolved questions, such as temporal evolution of this phenomena: the birth, growth, disappearance, and duration of thundercloud gamma rays, as well as the size of the electron acceleration region in the cloud.
To solve these questions, we need increased number of observation points to track moving thunderclouds, and started the Citizen science based multipoint observation campaign "Thundercloud Project.". With the cooperation of citizen supporters in this project, a small and portable radiation monitor, called "Cogamo (Compact Gamma-ray Monitor)", are deployed in Kanazawa City, Ishikawa Prefecture during the winter season, making a large-scale observation network. A Cogamo detector have a 5×5×15 cm CsI(Tl) scintillator coupled with a Hamamatsu Photonics MPPC photodetector, and can remotely monitor radiation data along with GPS signals and environmental sensor information. By increasing the area and density covered by this multi-point observation, we will be able to track thunderclouds and elucidate the mysteries of thunderclouds and gamma rays, such as (1) when electron acceleration in thunderclouds starts, how long it lasts, and how it ends, (2) in what types of thunderclouds electron acceleration occurs, and (3) whether accelerated electrons can trigger lightning discharges.
In fiscal year 2021, we have established an observation system of 50 Cogamo detectors in Ishikawa Prefecture and are performed observations from December to March. During this period, we have achieved remote real-time monitoring of gamma-ray glows using an automatic alert system. We also broadcast YouTube movie of a visible camera installed at the Tokyu Hotel in Kanazawa to capture thunderstorms above Cogamo detectors. Here we report the observation and analysis results for the year 2021.
As an example, two Cogamo detectors detected thundercloud gamma-ray glows along a moving cloud over eastern Kanazawa City at 14:20 JST on December 19, 2021. About 160 seconds after one Cogamo detectors detected an increase of about 400 gamma-ray photons, another Cogamo detector about 2 km away from the first one also recorded an event with about 140 photons. Comparing the data with the synthetic rainfall data from XRAIN published by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), this gamma-ray glow event is revealed to be coincided with the movement of the developing rain clouds. We also succeeded in capturing the same gamma-ray emitting cloud with the visible light camera. The camera shows moving clouds with low cloud base altitude, which is important information for understanding the characteristics of the gamma-ray glow.