The large-scale plasmaspheric density trough associated with the 24 May 2000
geomagnetic storm: IMAGE EUV observations and global core plasma modeling

M.L. Adrian and D.L. Gallagher
Science Directorate, SD50, NASA/Marshall Space Flight Center, Huntsville, AL  35812

J.L. Green
Space Sciences Data Operations Office, Code 630, NASA/Goddard Space Flight Center,
Greenbelt, MD  20771

B.R. Sandel
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ  85721


The IMAGE EUV imager observed a plasmaspheric density trough in association with a
geomagnetically active period on 24 May 2000.  In EUV, this density trough appears
as an Archimedes spiral extending from Earth's shadow to approximately 1800 MLT. 
We present an analysis of this density trough using simulated EUV images. 
Observational EUV images are subjected to edge analysis to establish the
plasmapause L-shell and the location of the density trough in terms of L-shell, MLT
extent, and radial width.  The plasmaspheric density distribution is modeled using
both static and dynamic models for the plasmasphere.  The background plasmasphere
is then numerically simulated using the 4-parameter plasmaspheric density model
contained within the Global Core Plasma Model (GCPM) [Gallagher et al., 2000] and
the Dynamic Global Core Plasma Model (DGCPM) [Ober et al., 1997].  Simulated EUV
images of the model plasmasphere are produced once an artificial density depletion,
matching the observed MLT extent and width, has been removed.  Once the azimuthal
extent and width of the trough have been simulated, the depth of the artificial
density depletion is iteratively adjusted to produce simulated EUV images that
approximate observation.  The results of this analysis and discussion of possible
origins for this density trough will be presented.

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Submitted to the Spring AGU Meeting, Boston, Massachusetts, 29 May - 2 June 2001