Measurement of TGE particle energy spectra: An insight in the cloud charge structure

Abstract

In this letter, we present for the first time the method to get insight into the charge structure of the thundercloud using simultaneously measured electron and gamma-ray energy spectra of the thunderstorm ground enhancement (TGE). We discuss and compare two main scenarios that can support the initiation of the relativistic runaway electron avalanches (RREA) in the thundercloud. One of the scenarios includes the emergence of the lower positive charged layer (LPCR). The LPCR is a short-living charge structure sitting on hydrometeors, which exhibit accidental charge reversals depending on temperature changes. LPCR can sustain a downwards directed near-surface electric field for several minutes, before falling down with precipitation. Recently, we launched on Aragats a large spectrometer, which is capable to measure energy spectra of electrons and gamma-rays in the energy range from 4 to 100 MeV. Comparison of energy spectra of electrons and gamma-rays makes it possible to scrutinize the LPCR emergence and estimate the height where the strong electric field that originates the RREA terminates.