Observation of the gradual increases and bursts of energetic radiation generated during winter lightning activity

Torii, Tatsuo  ; Sugita, Takeshi*; Muraki, Yasushi*

-ray dose-rate increase associated with thunderstorm activities was observed on the ground in winter. To investigate the fluctuation profile during winter thunderstorms, the energetic radiation was measured by using 4 set of radiation detectors (LPRCs). The LPRCs have a different response characteristic for the incident particle by mounting shield covers. Moreover, the electric field was measured at the same site by using a field mill. In the observation, the count-rate fluctuation which seem to originate from thunderstorm activity observed. The features obtained by the measurement and the analysis of the counters are as follows: It was observed that the radiation intensity began to increase from before several 10s in which the radiation burst is generated. The gradual fluctuation is caused mainly by the irradiation of photons with energy of several MeV. It was considered that the radiation burst attributed in the injection of high energy photons with the energy over 10MeV.