Abstract
During the winter thunderstorm season in Japan, a field campaign was conducted to observe radiation bursts associated with lightning discharges with the use of a NaI scintillator and a thin plastic scintillator (PS) which detects high energy electrons extensively. Two radiation bursts were recorded associated with an upward negative lightning stroke and an upward positive lightning stroke. In both cases, cloud discharges are recognized several milliseconds before the beginnings of their upward leaders. Count rates on the NaI began to increase at the beginnings of the cloud discharges, while that on the PS increased synchronized with the leaders and the lightning current. These results indicate that 1) high energy electron bursts were recorded on the ground associated with the leaders and the lightning currents and 2) not only negative breakdowns but also positive breakdowns cause runaway breakdown.
