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Wada, Yuki*; Enoto, Teruaki*; Nakamura, Yoshitaka*; Morimoto, Takeshi*; Sato, Mitsuteru*; Ushio, Tomoo*; Nakazawa, Kazuhiro*; Yuasa, Takayuki*; Yonetoku, Daisuke*; Sawano, Tatsuya*; et al.
Journal of Geophysical Research; Atmospheres, 125(4), p.e2019JD031730_1 - e2019JD031730_11, 2020/02
Times Cited Count：19 Percentile：85.61(Meteorology & Atmospheric Sciences)Wada, Yuki*; Enoto, Teruaki*; Nakamura, Yoshitaka*; Furuta, Yoshihiro; Yuasa, Takayuki*; Nakazawa, Kazuhiro*; Morimoto, Takeshi*; Sato, Mitsuteru*; Matsumoto, Takahiro*; Yonetoku, Daisuke*; et al.
Communications Physics (Internet), 2(1), p.67_1 - 67_9, 2019/06
Times Cited Count：35 Percentile：91.67(Physics, Multidisciplinary)Wada, Yuki*; Bowers, G. S.*; Enoto, Teruaki*; Kamogawa, Masashi*; Nakamura, Yoshitaka*; Morimoto, Takeshi*; Smith, D.*; Furuta, Yoshihiro*; Nakazawa, Kazuhiro*; Yuasa, Takayuki*; et al.
Geophysical Research Letters, 45(11), p.5700 - 5707, 2018/06
Times Cited Count：23 Percentile：78.54(Geosciences, Multidisciplinary)Torii, Tatsuo; Sugita, Takeshi; Kamogawa, Masashi*; Watanabe, Yasuyuki*; Kusunoki, Kenichi*
Geophysical Research Letters, 38(24), p.L24801_1 - L24801_5, 2011/12
Times Cited Count：58 Percentile：84.71(Geosciences, Multidisciplinary)We identify a migrating source of high energy radiation, lasting for several minutes, attributed to thunderstorm activities through the observations of radiation, atmospheric electric field, and meteorological radar echoes at several points. Our findings indicate that the energetic radiation is emitted continuously from a downward hemispherical surface without lightning, the bottom of which is about 300 m above sea level, and this source of radiation moves from north to south above the observation site at a speed of about 7 m/s. The radiation source probably moves along with the negatively charged region of the cloud at the height of around 1 km, because the estimated migration of the radiation source is consistent with the observed movement of atmospheric electric field variation between ground-based observation sites and with the wind speed and direction at about 1 km altitude. This movement implies that the intensive electric field produced by the charged region in the thundercloud generates a radiation source. In addition, our results suggest that the low altitude of radiation source is related to no lightning activity during the energetic radiation emission.
Torii, Tatsuo; Sugita, Takeshi*; Tanabe, Sachiko*; Kimura, Yoshihisa*; Kamogawa, Masashi*; Yajima, Kazuaki*; Yasuda, Hiroshi*
Geophysical Research Letters, 36(13), p.L13804_1 - L13804_4, 2009/07
Times Cited Count：50 Percentile：78.82(Geosciences, Multidisciplinary)Fluctuations of energetic radiation that seemed to be caused by a summer thunderstorm were observed at the top of Mt. Fuji. The largest of such fluctuations was gradual and lasted for about 20 minutes, and was found to be high-energy 
rays having a continuous energy spectrum up to 10 MeV or more. As for the feature of these fluctuations, it seems naturally that such fluctuations are caused by the bremsstrahlung photons generated by the energetic electrons produced continuously with an intense electric field in the thundercloud rather than originated in the process of lightning discharge.
Torii, Tatsuo; Sugita, Takeshi*; Tanabe, Sachiko*; Kimura, Yoshihisa*; Kamogawa, Masashi*; Yajima, Kazuaki*; Yasuda, Hiroshi*
Taiki Denki Gakkai-Shi, 3(1), p.111 - 112, 2009/00
Fluctuations of energetic radiation that were seemed to be caused by a summer thunderstorm activity were observed at the top of Mt. Fuji. The largest of such fluctuations was gradual and lasted for about 20 minutes, and was found to be high-energy rays having a continuous energy spectrum up to 10 MeV or more. As for the feature of these fluctuations, it seems naturally that such fluctuations are caused by the bremsstrahlung photons generated by the runaway electrons produced continuously with an intense electric field in the thundercloud rather than originated in the process of lightning discharge.
Torii, Tatsuo; Sugita, Takeshi*; Tanabe, Sachiko*; Kimura, Yoshihisa*; Kamogawa, Masashi*; Yajima, Kazuaki*; Yasuda, Hiroshi*
no journal, ,
Fluctuations of energetic radiation that were seemed to be caused by a summer thunderstorm activity were observed at the top of Mt. Fuji. The largest of such fluctuations was gradual and lasted for about 20 minutes, and was found to be high-energy rays having a continuous energy spectrum up to 10 MeV or more. As for the feature of these fluctuations, it seems naturally that such fluctuations are caused by the bremsstrahlung photons generated by the runaway electrons produced continuously with an intense electric field in the thundercloud rather than originated in the process of lightning discharge. The 5-inch NaI detector used in the observation was so sensitive to photons that it could not have differentiated electrons from photons even if high-energy electrons had been incident upon the detector. When conducting the analysis of energy spectrum, sufficient convergence was achieved in the calculation even in the case where only the sensitivity to photons was considered.
Torii, Tatsuo; Yasuda, Hiroshi*; Yajima, Kazuaki*; Sugita, Takeshi*; Tanabe, Sachiko*; Kimura, Yoshihisa*; Kamogawa, Masashi*
no journal, ,
Fluctuations of energetic radiation that were seemed to be caused by a summer thunderstorm were observed at the top of Mt. Fuji. The largest of such fluctuations was gradual and lasted for about 20 minutes, and was found to be high-energy rays having a continuous energy spectrum up to 10 MeV or more. As for the feature of these fluctuations, it seems naturally that such fluctuations are caused by the bremsstrahlung photons generated by the energetic electrons produced continuously with an intense electric field in the thundercloud rather than originated in the process of lightning discharge.
Torii, Tatsuo; Sugita, Takeshi*; Tsuchiya, Harufumi*; Tanabe, Sachiko*; Kimura, Yoshihisa*; Kamogawa, Masashi*; Yajima, Kazuaki*; Yasuda, Hiroshi*
no journal, ,
The dose rate of the -rays increases in association with the activities of the thunderstorm. They were observed on the ground in the winter season of Japan. As an observed result, the following two types of the radiation enhancements have been found during the winter thunderstorm activities; the gradual variation of photon intensity with energy of a few MeV, and the burst type of the radiation that is attributed to the injection of high energy photons with the energy over 10 MeV. Furthermore, fluctuations of energetic radiation that were seemed to be caused by a summer thunderstorm activity were observed at the top of Mt. Fuji. The largest of such fluctuations was gradual and lasted for about 20 minutes, and was found to be high-energy rays having a continuous energy spectrum up to 10 MeV or more.
