Feedback Between Electromagnetic Ion Cyclotron Waves And Ionospheric Outflows

Dr. Jay R. Johnson
Princeton University
Plasma Physics Laboratory
Monday, April 11, 4:00 PM
Abstract:
Energetic heavy ion outflows detected by satellites in the auroral region are commonly associated with electromagnetic ion cyclotron wave activity (1-100Hz) observed by the same spacecraft. Because the Poynting flux of the waves is into the ionosphere, the waves can provide an energization source for the concomitant ion heating. One difficulty with relating the ion outflows to the wave activity is the nonlocality of the heating process---much of the heating occurs between the ionosphere (where the ions originate) and the spacecraft. A common approach is to obtain a local heating rate from quasilinear theory based on the assumption that the wave spectral density is invariant along the auroral field lines. However, wave propagation and dissipation depends strongly on the heavy ion concentrations in the topside ionosphere as well as the collisional ionospheric model, and therefore the wave spectrum---and heating rate---at a given altitude is also strongly dependent on the plasma model. Thus, changes the plasma profiles change the wave propagation and heating rate. However, the heating rate determines the background plasma profiles. To account for this feedback, we successively iterate (1) a nonlocal wave propagation code (which solves the full electromagnetic equations including a realistic ionospheric model) based on specified background plasma profiles, and (2) a Monte Carlo simulation code to obtain the ion profiles based on heating rates obtained from the results of the wave propagation code. The method converges rapidly to a stable state. We present wave solutions and discuss dissipation of the wave energy along the field line through ion cyclotron resonance and Joule dissipation. We also discuss the implications of the feedback process for helium and oxygen distributions.

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