The structure of electric fields in the atmosphere still escapes from the detailed in situ measurements. Few balloon flights although providing us with overall knowledge of possible structures and strengths of the atmospheric electric fields, cannot reveal the dynamics of the intracloud electric field responsible for intense runaway electron fluxes and atmospheric discharges. To get insight into the charge structure of the thundercloud we use new key evidence – the fluxes of particles from the thundercloud registered on the earth’s surface, the so-called Thunderstorm Ground Enhancements – TGEs. TGEs originate from electron acceleration and multiplication processes in the strong electric fields in the atmosphere, and the intensity and energy spectra of electrons and gamma rays as observed at the Earth’s surface are directly governed by the charge structure of the cloud.