Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa41a1394s&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SA41A-1394
Physics
2411 Electric Fields (2712), 2415 Equatorial Ionosphere, 2431 Ionosphere/Magnetosphere Interactions (2736), 2736 Magnetosphere/Ionosphere Interactions (2431)
Scientific paper
At very low latitudes, close to the magnetic dip equator, plasma flows in the magnetosphere occur both vertically and in the north-south direction; they are assumed to be associated, by virtue of the MHD approximation above the ionosphere, with horizontal electric fields in the east-west direction. When these flows display temporal variations correlated with changes of magnetospheric convection at high latitudes, the conventional interpretation is that they represent E × B drifts produced by the electric field of the polar cap that has penetrated, with attenuated amplitude, down to the equator. This interpretation has both a general problem, incompatibility with the fundamental result for large-scale plasmas that flows produce electric fields but not vice versa, and a specific problem, non-uniqueness of the penetrating electric field calculated from the usual equations for the ionospheric potential: these require a boundary condition to be imposed at the equator, and it is entirely possible to choose constant potential as the boundary condition, thereby eliminating the east-west electric field. We show that the north-south flow is a direct consequence of magnetospheric convection flows in the northern and the southern hemispheres that collide at the equator; equivalently, the vertical flows result from magnetospheric convection in the equatorial plane that impinges upon the Earth. The east-west electric field is a consequence of both flows, not a cause. The flows occur as described because there is no significant magnetic stress in the magnetosphere that could deflect the magnetospheric convection away from the equator or around the Earth; this implies the boundary condition of no current across the equator, giving a unique solution for the electric potential in the ionosphere that is compatible with the presence of nonzero east-west fields.
Song Paul
Vasyliūnas Vytenis M.
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