Keywords:Energetic radiation, Thunderstorm, Mt. Fuji
We conducted the radiation and atmospheric electric field measurements at the summit of Mt. Fuji during the summer of 2013 and 2016. On July 26 and Aug. 5 of 2013 and Aug. 26 of 2016, the long burst of the energetic radiation was observed with 10 % enhancement. From the analysis of X-band MP radar, the radiation was observed tin the dissipation stage of thunderstorm. In all the cases, negative electric field (upward direction) was observed with approximately -30 kV/m, which is not enough to cause relativistic runaway electron avalanche (RREA). Therefore, plausible radiation source might be around the positively charged area in the thunderstorm.