Effects of ionospheric heating on feedback-unstable electromagnetic waves

Abstract

This paper presents first results from a numerical study of effects of ionospheric heating on the development of the ionospheric feedback instability in the auroral zone. The instability is driven by the electric field produced in the ionosphere by the closure of large-scale magnetic-field-aligned currents. This field heats ionospheric electrons and ions and changes the recombination rate and the ion mobility inside the ionospheric E-region. Self-consistent numerical simulations, based on the reduced two-fluid Magnetohydrodynamics (MHD) equations including active ionospheric feedback, demonstrate that these two quantities are very important parameters determining dynamics of the ionospheric feedback instability. In particular, simulations show that decrease in the ion mobility caused by heating can very efficiently suppress the instability, although the same effect also causes increase in the perpendicular electric field in the ionosphere. This result suggests that the ionospheric feedback instability should develop when ions in the ionosphere are cold, and it may explain why small-scale, intense electromagnetic structures and currents normally attributed to the instability are predominantly observed above the auroral ionosphere during the nighttime and during winter seasons. Simulations also demonstrate that heating of the ionospheric electrons can promote development of the instability, although this effect is not as strong as the effect of the ion heating. Copyright 2008 by the American Geophysical Union.