Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm41a1701m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM41A-1701
Physics
[2704] Magnetospheric Physics / Auroral Phenomena, [2712] Magnetospheric Physics / Electric Fields, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2736] Magnetospheric Physics / Magnetosphere/Ionosphere Interactions
Scientific paper
Auroral arcs are typically described in terms of an upward field-aligned current (FAC) sheet above the arc, connected by ionospheric Pedersen currents to a downward current sheet near the arc, while a divergence free Hall current electrojet (EJ) flows along the arc. A similar current topology is realized also on oval scale, where the arc associated FACs are replaced, in the morning and evening sectors, by the Region 1 and Region 2 currents, and the arc electrojet by the large scale convection electrojet. In the Harang region (HR), which makes the transition between the evening and morning sectors, the current configuration is often believed to consist of three FAC sheets, two downward FACs on the sides that feed a central upward FAC, again via ionospheric Pedersen currents. We show FAST observations indicating that in the HR the ionospheric current closure is sometimes dominated by the coupling between FAC sheets and electrojet currents, both on arc and oval scale. The FAC-EJ coupling can be achieved via Hall currents, implying that the Joule effect has little contribution to the energy dissipation in the ionosphere, achieved mainly by collisions of precipitating electrons energized in the auroral acceleration region. The current configuration at ionospheric level is consistent with azimuthal current closure in the magnetosphere, contributing to the asymmetry of the ring current in the dusk sector, and to the cancellation of the cross-tail current at substorm onset. The auroral current circuit appears as a mix of the 'Type 1' and 'Type 2' configurations introduced by Boström (1964), and may represent a new M-I coupling mode, relevant in particular for the HR.
Bunescu Costel
Karlsson Roland
Klecker Berndt
Marghitu Octav
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