Recent status of the GROWTH experiment; -ray observations at the coastal area of Japan sea

Tsuchiya, Harufumi 

Since 2006, the Gamma Ray Observation of Winter Thundercloud (GROWTH) experiment has been successfully operating at the coastal area of Japan sea. The GROWTH experiment aims at elucidating how particles in lightning and thunderclouds are accelerated to relativistic energies to produce rays and occasionally neutrons. According to observations done by the GROWTH experiment, it is found that there are two types of radiation bursts associated with thunderstorm activities. One is long bursts lasting for a few tens of seconds to a few minutes, being not clearly related to lightning. The other is short bursts in association with lightning. In this presentation we explain general properties of the two sorts of bursts and then show two new findings recently observed. One, which is categorized into long bursts, clearly exhibits a relationship between a long burst and an intra/inter-cloud discharge. The other is a combination of short bursts and long ones, providing a new insight into the nature of short bursts, with simultaneous detections of prompt rays and the annihilation ones. These -ray signals enabled us to confirm that photonuclear reactions certainly take place in a lightning discharge.