Electron density images of the middle and high latitude magnetosphere in
response to the solar wind

Jiannan Tu, Paul Song, Bodo W. Reinisch, Xueqin Huang, James L. Green, 
Harald U. Frey, and Patricia H. Reiff

Electron density images and plasma dynamics in the middle and high latitude
dayside magnetosphere are studied with the IMAGE/RPI remote measurements of the
electron densities along magnetic field lines, measured before and during a
magnetic storm when the solar wind and interplanetary magnetic field (IMF)
impinging on the magnetopause varied considerably. Several regions of different
density distribution characteristics, including plasmasphere, plasma trough,
sub-auroral/auroral density depletion, density enhancements in the aurora/cusp,
and polar cap, are identified in "twodimensional images", i.e., along the
satellite orbit and field lines. The plasma dynamics, such as the plasma
refilling in the outer plasmasphere and the plasma acceleration in the
aurora/cusp region are inferred from density gradients along the field lines. It
is shown that the densities and locations of the plasma regions vary in
accordance with the solar wind, particularly with the IMF variations for the
case examined. In the partial recovery phase of the magnetic storm when the IMF
was northward, the density depletion region expanded to wider latitude range and
extended to lower altitudes, with much lower densities than those in the density
depletion regions of the other RPI measurement periods. The density enhancements
associated with the aurora/cusp region were not visible, possibly because of the
diffusive nature of the dayside aurora and higher latitude location of the cusp
during this period. At the peak of the storm, characterized by a persistent
southward IMF Bz, all plasma regions moved to lower L shells. The results imply
that the solar wind/IMF effects should be included in any statistical study of
the electron density distributions in these regions.

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Submitted to Journal of Geophysical Research, July, 2005