Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm71b..02s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM71B-02
Physics
2407 Auroral Ionosphere (2704), 2704 Auroral Phenomena (2407), 2708 Current Systems (2409), 2712 Electric Fields (2411)
Scientific paper
As a first approximation the ionosphere can be thought of as a passive load for the magnetosphere, where currents and electric fields are imposed on the ionosphere by the magnetosphere. In this simple picture the ionosphere acts a both a mechanical and electromagnetic load. The reality is of course much more complex. The ionosphere is not a uniformly conducting medium, especially in the nightside, and the currents and electric fields imposed by the magnetosphere do not simply map to the ionosphere. Moreover, because of non-uniformities within the ionosphere, there will be feedback between the ionosphere and magnetosphere. Lastly, processes occurring on flux tubes at intermediate altitudes will also act to distort the mapping between the magnetosphere and ionosphere. The Fast Auroral Snapshot Small Explorer (FAST), with its high-resolution instrumentation, has explored these intermediate altitudes. FAST has demonstrated the presence of large-scale parallel potential drops, which correspond to a decoupling between magnetosphere and ionosphere in terms of electric field mapping. Moreover, FAST has shown the validity of the "Knight relation" in the upward current region. As a consequence the electric field pattern will be further distorted by the resultant conductivity gradients associated with the enhanced electron precipitation. These effects can be large locally, but the consequences of such non-ideal mapping on the more global aspects of magnetosphere-ionosphere coupling have yet to be assessed. FAST has also demonstrated the importance of parallel electric fields in the return current region, and again some degree of decoupling is expected. In the return current region waves are expected to play a more important role, and the relationship between downward current and parallel potentials is likely to be depend on a scaling law that incorporates wave effects. Last, FAST observations have demonstrated the importance of Alfvén waves for acccelerating electrons and heating outflowing ions, especially at the poleward edge of the auroral oval. Alfvén waves are the means by which changes in the magnetospheric drivers are transmitted to the ionosphere, but this evidence of wave-induced particle acceleration, and the possibility of ionospheric conductivity enhancements, again emphasizes the complexity of what at first glance appears to be a relatively simple interaction.
Carlson Carl W.
Elphic Richard C.
Strangeway Robert J.
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