Atmospheric gamma-ray and neutron flashes

Gamma-ray pulses are calculated from 2D numerical simulations of an upward atmospheric discharge in a self-consistent electric field using the multigroup approach to the kinetics of relativistic runaway electrons (REs). Computed y-ray numbers and spectra are consistent with those of terrestrial gamma-ray flashes (TGFs) observed aboard spacecrafts. The RE flux is concentrated mainly within the domain of the Blue Jet fluorescence. This confirms that exactly the domain adjacent to a thundercloud is the source of the observed y-ray flashes. The yield of photonuclear neutrons is calculated. One y-ray pulse generates similar to 1014-10(15) neutrons. The possibility of the direct deposition of REs to the detector readings and the origin of the lightning-advanced TGFs are discussed.