  Relativistic runaway electron avalanches (RREA) accelerated by thunderstorm
large-scale electric fields are one of the sources of atmospheric gamma
radiation. In strong electric fields, RREAs can multiply by the relativistic
feedback. Infinite relativistic feedback makes avalanches self-sustainable and
hypothetically can cause a terrestrial gamma-ray flash (TGF). This paper
introduces a kinetic approach to study the relativistic feedback caused by
positrons since positron feedback dominates for the directly observed electric
field strengths. With this approach, the criterion for infinite positron
feedback within thunderstorms is derived. Discovered criterion allows obtaining
the thunderstorm electric field parameters required for infinite positron
feedback for any altitude. The possibility of derived thunderstorm conditions
is discussed.
