Specifying Plasma Density Profiles for Plasmasphere Refilling Using IMAGE RPI 
Observations

P. Song, J. Tu, B. W. Reinisch, J. L. Green, and X. Huang


Sounding measurements from the radio plasma imager (RPI) on the IMAGE satellite are
used to derive electron density distributions along magnetic field lines in the
nightside plasmasphere and plasma trough for three mid-latitude passes. These passes
occurred during 1) a magnetic storm, 2) a prolonged quiet time, and 3) a sudden
commencement of a storm, respectively. It is found that the density profiles of
filled (in the inner plasmasphere) and depleted (in the plasma trough or outer
plasmasphere) flux tubes have different field line dependence. A multi-variant least
square fit with a simple analytical function is used to model the density profiles.
The fitting parameters in the function define the field line dependence of a density
profile, i.e., the steepness of the density profile at high latitudes and the
flatness at low latitudes. In each pass the density profiles along the filled and
depleted flux tubes can be well modeled with the selected functional form, with two
different sets of fitting parameter values for filled and depleted flux tubes. For
the three passes examined, the fitting parameter values are not sensitive to the
geomagnetic activity for the inner plasmasphere density profiles but vary slightly
for the plasma trough or outer plasmasphere density profiles from case to case. The
equatorial densities extrapolated from the measured density profiles approximately
have a power law relation with L values. The results suggest that the selected
function has potential of being able to construct realistic global empirical
plasmasphere/plasma trough models. Furthermore, it is now feasible to empirically
determine the density profiles along the depleted flux tubes for plasmasphere
refilling studies.

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European Geosciences Union General Assembly, Vienna, Austria, 2-7 April 2006