Particle bursts from thunderclouds: Natural particle accelerators above our heads

Strong electrical fields inside thunderclouds give rise to fluxes of high-energy electrons and, consequently, gamma rays and neutrons. Gamma rays and electrons are currently detected by the facilities of low orbiting satellites and by networks of surface particle detectors. During intensive particle fluxes, coinciding with thunderstorms, series of particle bursts were detected by the particle detectors of Aragats Space Environmental Center at an altitude of 3250 m. We classify the thunderstorm ground enhancements in 2 categories, one lasting microseconds, and the other lasting tens of minutes. Both types of events can occur at the same time, coinciding with a large negative electric field between the cloud and the ground and negative intracloud lightning. Statistical analysis of the short thunderstorm ground enhancement bursts sample suggests the duration is less than 50 mu s and spatial extension is larger than 1000 m(2). We discuss the origin of thunderstorm ground enhancements and its connection to the terrestrial gamma flashes detected by orbiting gamma-ray observatories.