Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23b1701l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM23B-1701
Physics
2463 Plasma Convection (2760), 2721 Field-Aligned Currents And Current Systems (2409), 2736 Magnetosphere/Ionosphere Interactions (2431), 2740 Magnetospheric Configuration And Dynamics, 2776 Polar Cap Phenomena
Scientific paper
Intense duskside ionospheric flows occurring equatorward of the discrete auroral precipitation zone have been attributed to large electric fields resulting from partial ring current injections. In this picture the driver is the ion injection that feeds the Region 2 currents which in turn cause the electric field. Alternatively, one may take the view that the return flow at dusk is favored energetically by the coupled magnetosphere-ionosphere system. In this energetics view, the upward Region 2 at dawn corresponds to discrete aurora and enhanced conductance on closed field lines on the dawn side, whereas the downward Region 2 at dusk does not contribute as substantially to enhancing the duskside conductance. The energy dissipation associated with a given flow is proportional to the conductance. Thus, it is energetically more favorable for the coupled system to send more return flow to the dayside at dusk than at dawn. In this paper we assess whether there is a persistent dawn dusk asymmetry in the return flow relative to the Birkeland current location and intensity. Birkeland currents derived from the Iridium Satellite constellation, augmented with DMSP F13 magnetic field data are used to place DMSP F13 drift meter data in the context of both the global and local Birkeland currents. Using events from the Iridium stable currents database of Anderson et al. (2008), we identified 59 events with high quality drift observations during southward IMF. The events are divided into two ranges of IMF intensity and five IMF clock angle bins. We order the data in latitude relative to the peak Region 1 current density. There is a persistent suppression of the dawn return flows relative to those at dusk regardless of IMF By or IMF intensity. This result indicates that the return flow predominantly occurs through the evening closed field line region, consistent with the above energetics picture of return flow in the coupled system.
Anderson Benjamin J.
Bodurtha K. E.
Korth Haje
Larson Richard
Wilson Grant
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