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Long-duration γ ray emissions from 2007 and 2008 winter thunderstorms

Tsuchiya, H. and Enoto, T. and Yamada, S. and Yuasa, T. and Nakazawa, K. and Kitaguchi, T. and Kawaharada, M. and Kokubun, M. and Kato, H. and Okano, M. and Makishima, K. (2011) Long-duration γ ray emissions from 2007 and 2008 winter thunderstorms. Journal of Geophysical Research D, 116 (D9). D09113. ISSN 0148-0227.

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The Gamma-Ray Observation of Winter Thunderclouds (GROWTH) experiment, consisting of two radiation detection subsystems, has been operating since 2006 on the premises of Kashiwazaki-Kariwa nuclear power plant located at the coastal area of Japan Sea. By February 2010, GROWTH detected seven long-duration γ ray emissions associated with winter thunderstorms. Of them, two events, obtained on 13 December 2007 and 25 December 2008, are reported. On both occasions, all inorganic scintillators (NaI, CsI, and BGO) of the two subsystems detected significant γ ray signals lasting for >1 min. Neither of these two events were associated with any lightning. In both cases, the γ ray energy spectra extend to 10 MeV, suggesting that the detected γ rays are produced by relativistic electrons via bremsstrahlung. Assuming that the initial photon spectrum at the source is expressed by a power law function, the observed photons can be interpreted as being radiated from a source located at a distance of 290–560 m for the 2007 event and 110–690 m for the 2008 one, both at the 90% confidence level. Employing these photon spectra, the number of relativistic electrons is estimated as 10^(9)–10^(11). The estimation generally agrees with those calculated on the basis of the relativistic runaway electron avalanche model. A GROWTH photon spectrum, summed over three individual events including the present two events and another reported previously, has similar features including a cutoff energy, to an averaged spectrum of terrestrial γ ray flashes.

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Additional Information:© 2011 American Geophysical Union. Received 7 October 2010; accepted 23 February 2011; published 14 May 2011. We thank members of radiation safety group at Kashiwazaki‐Kariwa power station, Tokyo Electric Power Company, for supporting our experiment. This work is supported in part by the Special Research Project for Basic Science at RIKEN, titled “Investigation of Spontaneously Evolving Systems,” and the Special Postdoctoral Research Project for Basic Science at RIKEN. The work is also supported in part by Grant-in-Aid for Scientific Research (S) 18104004 and Grant-in-Aid for Young Scientists (B) 19740167.
Funding AgencyGrant Number
Tokyo Electric Power CompanyUNSPECIFIED
RIKEN Special Research Project for Basic ScienceUNSPECIFIED
RIKEN Special Postdoctoral Research Project for Basic ScienceUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)18104004
Japan Society for the Promotion of Science (JSPS)19740167
Subject Keywords:gamma rays; thunderclouds; particle acceleration
Issue or Number:D9
Record Number:CaltechAUTHORS:20110531-153842179
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Official Citation:Tsuchiya, H., et al. (2011), Long‐duration g ray emissions from 2007 and 2008 winter thunderstorms, J. Geophys. Res., 116, D09113, doi:10.1029/2010JD015161.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23849
Deposited By: Jason Perez
Deposited On:01 Jun 2011 22:36
Last Modified:03 Oct 2019 02:50

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