Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmsm41a..02j&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #SM41A-02
Physics
2431 Ionosphere/Magnetosphere Interactions (2736), 2487 Wave Propagation (0689, 3285, 4275, 4455, 6934), 2704 Auroral Phenomena (2407), 7867 Wave/Particle Interactions (2483, 6984)
Scientific paper
Satellites in the auroral region often detect energetic heavy ion outflows together with electromagnetic ion cylotron wave activity (1-100Hz). Because the Poynting flux of the waves is directed into the ionosphere the waves can energize ionospheric ions at lower altitude leading to ion outflow from the topside ionosphere. 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 practice is to assume a heating rate based upon the spectrum observed locally by the satellite. However, nonlocal wave solutions suggest that propagation and dissipation of the wave spectrum depends sensitively on the heavy ion plasma profiles in the topside ionosphere as well as the collisional ionospheric model. Consequently, the heating rate is strongly dependent on the plasma density profile. Because the heating rate determines the plasma profiles and the background profiles determine the heating rate, it is necessary to account for the feedback in a self-consistent manner. We successively iterate (1) a wave propagation code based on background plasma profiles (which solves the full electromagnetic equations including a realistic ionospheric model) 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. These wave solutions include the possibility of mode conversion among the propagating wave modes, dissipation at the cyclotron resonance, and collisional dissipation and reflection of the wave in the ionosphere. The method converges rapidly to a stable state, and the results suggest that the temporal evolution of the plasma profiles may involve a two-step process where helium is first heated then oxygen. We also discuss how primary cyclotron resonant heating differs from nonlinear stochastic ion heating that can occur at lower frequency in large amplitude Alfven waves. Finally, we discuss the challenges of incorporating such physical processes in global models.
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