The criterion for self-sustaining production of relativistic runaway electron avalanches by the positron feedback in thunderstorms

Abstract

Relativistic runaway electron avalanches (RREA) occurring in thunderstorm large-scale electric fields are one of the sources of atmospheric gamma radiation. Relativistic feedback is the generation of RREAs by positrons or backscattered gamma rays of the previously produced RREAs. In strong electric fields, relativistic feedback can make RREAs self-sustainable that hypothetically can cause a terrestrial gamma-ray flash (TGF). This paper introduces a kinetic approach to study the positron relativistic feedback, which is predominant for the directly observed conditions within thunderstorms. The criterion for self-sustaining production of RREAs by the positron feedback in thunderstorms is derived. The discovered criterion allows one to obtain the parameters of the thunderstorm electric field required for self-sustaining RREA development with positron feedback for any altitude. It is shown that the derived conditions of self-sustainable RREA development are not achieved for the parameters of electric field observed in real thunderclouds.