Relativistic Feedback Rates in the Presence of the Geomagnetic Field

It has been shown that relativistic feedback allows runaway electron avalanche discharges in the atmosphere to become self-sustaining. Since relativistic feedback is also capable of increasing the flux of runaway electrons and x-rays by a factor of 10^13 under certain thunderstorm conditions, it provides a plausible mechanism for the generation of terrestrial gamma-ray flashes (TGFs). Relativistic feedback has been previously investigated without the presence of a geomagnetic field. However, for altitudes near the tops of thunderclouds and above, the effects of the magnetic field on the feedback rates can be important in some cases. We use detailed three-dimensional Monte Carlo simulations of runaway electron avalanches in the presence of the earth's magnetic field to investigate the field's impact on relativistic feedback. In particular, we shall present results for fundamental parameters such as avalanche lengths, feedback factors, and the feedback threshold, above which an electric field is unstable.