Electrical structure of the thundercloud and operation of the electron accelerator inside it

Abstract The most powerful particle accelerators operating in thunderclouds send in direction of the earth's millions and millions of electrons, gamma rays, and rarely neutrons. The emerging electrical structures in the atmosphere which make it possible to accelerate seed electrons from an ambient population of cosmic rays up to ≈70 MeV are still an area of intensive research. We discuss the main scenarios of the thundercloud charge structure supporting the emergence of an electric field strong enough to help electrons run away and create electron avalanches (RREA). After coming out of the accelerating electric field in the thundercloud, the RRE avalanche significantly attenuates and reaching the earth's surface is measured by the particle detectors and spectrometers as thunderstorm ground enhancement (TGE). Energy spectra of the measured fluxes of electrons and gamma rays can be used to reveal the charge structures giving rise to RREA. We perform simulation of the RREA development in the thundercloud with CORSIKA code and compare energy spectra of RREA corresponding to different configurations of the intracloud electric field with energy spectra of TGE measured in summer 2020. We invoke also additional evidence, namely the hydrometeor density profiles obtained with the weather research and forecast model (WRF) to confirm disclosed charge structures.