Low-Frequency Ionization-Driven Instability of an Auroral Arc Model.

摘要

The low-frequency (time scales of tens of seconds) dynamics of the auroral ionosphere differs from that of the nonauroral ionosphere by the presence of strong, unstable space-and-time-dependent ionospheric ionization produced by precipitating auroral electrons. If recombination is relatively unimportant (as at high ionospheric heights), we show that in general transport processes cannot remove this ionization as fact as it is created, and no equilibrium is possible. We investigate these nonequilibrium phenomena in the context of a nonlinear adiabatic auroral model, which has previously been studied in static situations. We give linearized local pertubation analysis of what amounts to a current-driven E X B GRADIENT-drift instability with an ionization source, as well as some exact nonlinear solutions valid in a finite but limited spatial region. These solutions show continuing motion of auroral potential and plasma density as the aurora tries to shift its ionization problems from one place to another. The analysis gives clues to the possibility of generation of chaos and of fine-scale spatial structure. (jhd)