Simulating plasmaspheric field-aligned density profiles measured with IMAGE/RPI: 
Effects of plasmasphere refilling and ion heating

J.-N. Tu , J. L. Horwitz, P. Song, X.-Q. Huang, and B. W. Reinisch, 
and P. G. Richards


The radio plasma imager (RPI) on board the IMAGE satellite measures electron
density profiles along magnetic lines through radio sounding techniques. We
simulate three density profiles measured by the RPI on 8 June 2001 using the
field line interhemispheric plasma (FLIP) model and compare the modeled density
profiles with observed profiles. While careful consideration of depletion of
flux tubes followed by refilling over several days allows fair agreement between
simulated and measured densities around the equator, the simulated densities in
the off-equator regions remain significantly lower than those measured for all
simulated flux tubes. It is shown that direct heating of ions in the
plasmasphere during the plasmasphere refilling, in addition to heating through
Coulomb collisions with hotter plasmaspheric electrons, can improve the
agreement in the off-equator regions. The enhanced ion pressure in the high
altitude part of magnetic field line due to the ion heating impedes the
ionospheric inflow from both hemispheres toward the equator, giving rise to
decreased transport of ionospheric ions into the equatorial region and thus
increased density gradient along the magnetic field line.

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Journal of Geophysical Research, 108(A1), 1017, doi:10.1029/2002JA009468, 2003.