Effect of Thunderstorm Electric Field on the Cosmic Ray Secondary Particle Energy at LHAASO

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) is located in Daocheng, Sichuan. Featured with frequent thunderstorms in summer seasons, it is beneficial to study the influence of atmospheric electric field on cosmic rays during thunderstorms. In this paper, Monte-Carlo simulations are performed to study the effect of thunderstorm electric field on the cosmic ray secondary electron energy at LHAASO. The energy distribution of electrons changes under the action of electric field. In the low energy region, the total number of electrons increases significantly, while at high energies, it does not change obviously. In the electric field of 1700V·cm−1 (above the critical field of the Relativistic Runaway Electron Avalanche (RREA) process), the electrons with an energy less than 120MeV can be accelerated. When the energy is below 60MeV, the number of electrons increases exponentially with an amplitude up to about 2252%. It is consistent with the theory of RREA. When the electric field strength is 1000V·cm−1 (below the threshold of the RREA process), the electrons with an energy less than 70MeV are accelerated, and their number increases significantly, but the increase (about 86%) is far lower than that of the critical field of the RREA process. The physical mechanism for accelerating the cosmic ray secondary particles by the thunderstorm electric field is discussed in the case when the electric field is less than the runaway electric field. These results may provide important information for studying the variations of cosmic ray intensity on the LHAASO detection surface during thunderstorms.