Positron acceleration in thunderstorms

Abstract

Thunderstorm Ground Enhancements (TGEs) are known manifestations of relativistic runaway electron avalanches (RREAs) developing inside thunderclouds. However, the role of positrons in TGEs and their relationship to thundercloud charge structure remain poorly understood. We report time resolved observations of intense positron fluxes detected at the Aragats Observatory on 16 17 May 2026 during strong thunderstorms. Two of the three events were characterized by a positive near surface electric field (NSEF), graupel precipitation, a low cloud base, and low-to-moderate enhancement of gamma ray and electron fluxes measured by SEVAN and STAND3 detectors. The third event is a classical electron TGE considered for comparative purposes. All events show moderate to strong enhancement of the 511 keV annihilation line, along with enhanced radon progeny gamma ray lines. We observe a temporal separation between the electron and gamma ray TGE peak and the positron flux maximum. To explain these observations, we introduce a dual dipole electrodynamic model. The large scale electron dipole comprises the main negative thundercloud layer and its broad positive mirror charge induced at the Earths surface, producing ordinary TGEs. Simultaneously, a localized positron dipole forms from the LPCR, with its negative mirror charge directly beneath the LPCR footprint. This lower dipole accelerates positrons downward while decelerating electrons entering the same region. These results establish positron TGEs as a new subclass of atmospheric high energy phenomena and provide direct evidence of localized positron acceleration in the lower atmosphere.