Simulations of the secondary cosmic ray propagation in the thunderstorm atmospheres resulting in the Thunderstorm ground enhancements (TGEs)

GEANT4 simulations of the propagation of electrons in the thunderstorm atmospheres were performed to explain the Thunderstorm Ground Enhancements (TGEs), detected by the particle detectors of the Aragats Space Environmental Center (ASEC) operating at altitude 3200 m on slopes of Mt. Aragats in Armenia. The charged particle propagation and multiplication processes were simulated in the uniform electric fields of different strengths and elongation. The Gamma ray, electron and neutron energy spectra were obtained on the exit of the electrical field and beneath. Simulation results prove existence of 2 mechanisms of particle enhancements, first connected with electron – gamma ray avalanche process; and the second – with modification of energy spectra of particles in the strong electrical fields of the thunderclouds. The avalanche process can multiply number of electrons and gamma rays by several orders of magnitude well above the cosmic ray background in the energy range up to 40MeV; the energy spectra modifications lead to a few percent enhancements in the energy range up to 100MeV, as well as to depletion of the high-energy muon flux. Consequently the energy spectra at low energy are better fitted by exponential law; at high energies – by the power law.