Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm13a1671m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM13A-1671
Other
2736 Magnetosphere/Ionosphere Interactions (2431), 2753 Numerical Modeling, 2760 Plasma Convection (2463), 7827 Kinetic And Mhd Theory
Scientific paper
Acceleration of ionospheric oxygen above the polar ionosphere and its further transport to the plasmasheet has been a matter of research for more than two decades. Guiding center particle tracing in external magnetic and electric field has demonstrated that oxygen ions are centrifugally accelerated, especially in regions of strong magnetic field curvature such as the cusps. Direct observations of the centrifugal acceleration are difficult but possible, and have shown that this term in the field-aligned motion of guiding centers may be significant. On the other hand, it is unclear how bulk properties of the oxygen fluid are influenced by centrifugal acceleration. Is the oxygen fluid accelerated as a whole or is it heated? Is the heating anisotropic? Do relaxation processes, e.g. wave-particle interactions, influence the parallel transport by isotropizing the distribution function? Whereas there have been observational studies that addressed these questions, we take a different approach and investigate the oxygen transport using a multi-fluid MHD model. The model implies a Maxwellian particle distribution function and therefore limits the possible physical scenarios to those where the role of relaxation processes is significant. We simulate a number of idealized configurations with constant southward interplanetary magnetic field and investigate the bulk magnetosphere properties of the oxygen fluid that originates in the ionosphere (bulk speeds, plasmasheet pressure and density, number flux into the plasmasheet) as a function of the strength of magnetospheric convection. The ion source is included by juxtaposing an empirical model of thermal ion population based on Akebono observations and more energetic dayside cusp outflow based on empirical relation between the incoming Pointing flux and the outflowing particle flux (the "Strangeway" formula). By qualitatively comparing our results with available observations, we attempt to shed the light on the questions posed above.
García K. S.
Hughes Jeffrey W.
Lyon John G.
Merkin Viacheslav
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