Interpreting Local and Remote RPI/IMAGE Plasmaspheric Electron Density 
Measurements using a Global Plasmasphere-Ionosphere Model

Phillip A. Webb
NRC NASA/Goddard Space Flight Center, Code 692
Greenbelt, Maryland 20771   USA

Robert F. Benson
NASA/Goddard Space Flight Center, Code 692
Greenbelt, Maryland 20771   USA

Bodo W. Reinisch
Center for Atmospheric Research
University of Massachusetts at Lowell
Lowell, Massachusetts 01854   USA

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite is 
currently in a highly inclined elliptical orbit that takes it between altitudes 
of 1000 km and seven Earth radii. During each 14.2 hour orbit, IMAGEÕs 
instruments have the opportunity to observe the plasma distribution from the 
topside ionosphere to beyond the plasmapause. One such instrument carried by 
IMAGE is the Radio Plasma Imager (RPI). Using the RPI, the local electron 
density Ne can be separately calculated from plasma resonances stimulated 
during active soundings and natural emissions received during the passive 
recording of dynamic spectrograms. An along-orbit Ne profile can be obtained 
for each orbit by calculating Ne from these active and passive measurements. 
Furthermore, the active RPI soundings often produce reflection traces that can 
be converted into Ne profiles along the local field line into both hemispheres 
using inversion and ray-tracing techniques. Both these types of Ne profiles can 
be compared to the predictions of plasmaspheric models.

The theoretical-based Global Plasmasphere Ionosphere Density (GPID) model has 
been developed by the first author to simulate the global scale evolution of 
the ion and electron number densities in the plasmasphere. Combined with the 
latest version of the International Reference Ionosphere (IRI), GPID can model 
the dynamic emptying caused by geomagnetic storms and the following refilling 
of the plasmasphere. The accuracy of the GPID will be ascertained by comparing 
the models predictions with RPI derived Ne profiles across a variety of 
geomagnetic L-shells and various geomagnetic storm conditions.

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To be presented at the Western Pacific Geophysical Meeting, 
Wellington, New Zealand, 9-12 July 2002.