Plasma Flow Channels at Dawn/Dusk Polar cap Boundaries: Momentum Transfer on old Open Field Lines and the Roles of IMF By and Conductivity Gradients

Details Plasma Flow Channels at Dawn/Dusk Polar cap Boundaries: Momentum Transfer on old Open Field Lines and the Roles of IMF By and Conductivity Gradients Plasma Flow Channels at Dawn/Dusk Polar cap Boundaries: Momentum Transfer on old Open Field Lines and the Roles of IMF By and Conductivity Gradients

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23b1706s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM23B-1706

Physics

2721 Field-Aligned Currents And Current Systems (2409), 2731 Magnetosphere: Outer, 2776 Polar Cap Phenomena, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

Using DMSP F13 data we investigate the newly discovered channels of enhanced antisunward convection occurring at the dawn (0600-0900 MLT) or dusk (1500-1800 MLT) flanks of the polar cap for the different combinations of IMF By polarity, hemisphere and the dawn/dusk sides. Dawn-side cases occur for the following combinations of hemisphere (NH/SH) and By polarity: NH-dawn/By > 0 and SH-dawn/By < 0 . The dusk-side cases are: NH-dusk/By < 0 and SH-dusk/By > 0 . The flow channels are placed in the context of particle precipitation regimes/boundaries and ionospheric conductivity gradients. They are found to be threaded by "old open field lines" characterized by polar rain precipitation. In the dawn-side cases (NH-dawn/By > 0 and SH-dawn/By < 0 ) the polar rain contains the "solar wind strahl" component. The convection enhancement is attributed to the Pedersen current closure of Birkeland currents poleward of the R1/R2 currents. This is momentum transfer from the solar wind via dynamo action at the high-latitude boundary layer (HBL). The conductivity gradient at the polar cap boundary contributes to establishing the convection channel and the enhancementent of the dawn-dusk convection asymmetry extending beyond the dawn-dusk terminator during intervals of nonzero IMF By component. The HBL - ionosphere coupling via Birkeland currents is a source of dawn-dusk convection asymmetry and Svalgaard - Mansurov effect which comes in addition to the effect of magnetic tension acting on "newly open field lines".

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