On the Divergence of the Auroral Electrojets

Details On the Divergence of the Auroral Electrojets On the Divergence of the Auroral Electrojets

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm41c..06m&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM41C-06

Physics

[2463] Ionosphere / Plasma Convection, [2704] Magnetospheric Physics / Auroral Phenomena, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2790] Magnetospheric Physics / Substorms

Scientific paper

The current configuration in the auroral region is assumed to consist typically of downward and upward field-aligned current (FAC) sheets, connected in the ionosphere by meridional Pedersen currents, while divergence free electrojets (EJs) flow azimuthally as Hall currents. By using the newly developed ALADYN (auroral arc electrodynamics) technique, one can investigate the actual divergence of the auroral electrojets, by using observed satellite data. Examination of FAST data suggests that this divergence can be significant over certain latitude ranges, comparable with the FAC density. Direct FAC-EJ coupling appears to contribute to the ionospheric current closure not only during active times, as already known, but also during rather quiet periods. The quiet time FAC-EJ coupling is presumably achieved by the Pedersen component of the electrojet, driven by the tangential electric field. This is more likely realized inside or near the Harang region, where the azimuthal electric field is often significant. During active intervals and possible reconfigurations of the auroral current circuit, our investigation suggests that the FAC-EJ coupling can also be achieved by Hall currents. The FAC coupling to Hall currents may play a key role in the rise and fall of the electrojet current system and thus it can be an important dynamic agent of magnetosphere-ionosphere coupling. This mechanism received comparatively much less attention than the dynamic coupling of the FAC to Pedersen currents, associated with Alfvén waves bouncing along the flux tube. We conclude by exploring the integrated evolution of the ionospheric current closure and Cowling mechanism, in a tentative scenario of the auroral arc during the substorm cycle.

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