Nonlinear evolution of thermal self‐focusing instability in ionospheric modifications at high latitudes: Aspect angle dependence

Abstract

A first simulation study for the nonlinear evolution of the thermal self‐focusing instability at high latitudes to examine the dependence of the nonlinear effects on the direction of the heater beam is presented. We demonstrate that due to a local heating of the F region anisotropic plasma, field‐aligned bunch‐scale structures with a strong enhancement of the electron temperature and negative density perturbations inside these structures are developed. The electron temperature increases up to more than 200% of the background when the incident beam is near the magnetic zenith, as observed in the heating experiment at the EISCAT high‐latitude facility (Rietveld et al., 2003). The values of the simulated electron temperature enhancements show a strong dependence on the heater beam direction that is in very good agreement with the EISCAT observations.