Observation and a Monte Carlo Analysis of the Energetic Radiation Associated with Winter Thunderstorm Activities in Japan.
Abstract
Gamma ray dose-rate increases associated with winter thunderstorm activities have been observed at the coastal area of the Sea of Japan.The following features are clarified from the measured data obtained by environmental radiation monitors: 1. Almost all dose-rate increases during thunderstorms are from several to several 10 times of the background levels at each monitoring point. 2. The rise time of the dose-rate enhancement is about several ten seconds. 3. The affected areas of the enhanced radiation seemed to be quite local, because in many cases, only one or two of the monitors situated several hundred meters away from each other showed dose-rate increases. 4. The starting time of the dose-rate increase of two monitors at a position several 100 meters away is not always be simultaneously, and time lags of ten seconds are sometimes observed. 5. From the indicated values measured by two type detectors (NaI(Tl) scintillator, Ionization Chamber) of the monitor, this suggests that energetic radiation (several MeV) might be emitted at the time of dose-rate increasing. In order to investigate the generation of energetic radiation which originates in thunderstorm electric fields, we have calculated the behavior of secondary cosmic rays (electromagnetic component; muon) in electric fields with Monte Carlo method. In the calculation, the electron and photon fluxes have increased greatly in the region where the field strength exceeds about 280 P(z) kV/m-atm, where P(z) is the atmospheric pressure (atm) at altitude z (m),.and these energy spectra show a large increase in the energy region up to a few tens of MeV. We have also carried out the Monte Carlo calculations of the beta and gamma rays emitted by radon progenies in thunderstorm electric fields. By the calculation for the radon progeny, the electron flux shows notable increases in the strong electric field region, while the photon flux does not fluctuate significantly. As well as the secondary cosmic rays, the radon progeny products form a large part of the energetic charged particles in the atmosphere. Therefore, they can serve as the source of a considerable amount of runaway electrons, through their ionization process with air molecules. These results indicate that the production of energetic electrons plays an important role in the intensive ionization of the air, and as a result a significant growth of electric conductivity in thunderstorm electric fields. These productions may also induce the lightning discharge by these processes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFMAE33A0945T
- Keywords:
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- 0305 Aerosols and particles (0345;
- 4801;
- 4906);
- 2104 Cosmic rays;
- 3304 Atmospheric electricity;
- 3324 Lightning