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Ann. Geophys., 21, 2147-2154, 2003
www.ann-geophys.net/21/2147/2003/
© European Geosciences Union 2003
The local-time variation of the quiet plasmasphere: geosynchronous observations and kinetic theory
M. A. Reynolds1, G. Ganguli2, Y.-J. Su3, and M. F. Thomsen4
1Department of Physical Sciences, Embry-Riddle University, 600 S. Clyde Morris Blvd., Daytona Beach, FL 32114, USA
2Beam Physics Branch, Plasma Physics Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA
3Laboratory for Atmospheric and Space Physics, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303, USA
4Space and Atmospheric Sciences Group, NIS-1, MS-D466, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Abstract. The quiet-time structure
of the plasmaspheric density was investigated using observations of the Los
Alamos geosynchronous satellites, and these observations were compared with
theoretical predictions of the quasi-static local-time variation by a kinetic
model. It was found that the coupling to the ionosphere (via the local-time
variation of the exobase) played a key role in determining the density
structure at 6.6 RE . The kinetic model predicts that most of
the local-time variation at geosynchronous orbit is due to the variation of the
exobase parameters. During quiet times, when the convection electric field is
dominated by the corotation field, the effects due to flux-tube convection are
less prominent than those due to the exobase variation. In addition, the
kinetic model predicts that the geosynchronous plasmaspheric density level is
at most only 25% of saturation density, even when geomagnetic activity is low.
The low night-time densities of the ionospheric footpoints, and the subsequent
long trapping time scales, prevent the equatorial densities from reaching
saturation.
Key words. Magnetospheric physics
(magnetosphere-ionosphere interactions; plasma convection; plasmasphere)
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