Measurements and Modeling of Ionosphere-Plasmasphere Transport

Sandel, B.R., Denton, M.H.


A fundamental aspect of the coupling between Earth's ionosphere and inner
magnetosphere is the flow of ionospheric plasma that supplies material to the
plasmasphere. Using global observations of the He+ column abundance made by the
IMAGE Extreme Ultraviolet Imager, we investigate refilling of the plasmasphere
after erosion events associated with geomagnetic storms. To minimize the
confounding effects of phenomena other than refilling, we first focus on an
usually quiet period of several days beginning on 27~June 2001. Just prior to
this time, a moderate erosion event moved the plasmapause inward to L=3--4.
During the next 3 days, the plasmasphere refilled so that the plasmaspause moved
outward past geosynchronous orbit. For this and other similar study periods, we
compare the He+ column abundances inferred from the EUV images with the
predictions of the SUPIM model. The model solves the equations of continuity,
momentum and energy balance that describe the physical and chemical processes
occurring along closed field lines, and output from the model includes the He+
abundance. Comparing the model results to the azimuthally-averaged measurements
shows generally good agreement, both in the rates of refilling as a function of
radial distance and in the final shape of the radial profile of He+ column
abundance. A more-detailed view, including analysis of azimuthal structure in
the EUV images, suggests that the refilling rate is not always uniform in
azimuth.

_______________
Fall Meeting, American Geophysical Union, San Francisco, U.S.A., 
5-9 December 2005