Simulation Study of Plasmaspheric Density Distributions and High-latitude
Ion Transport Observed by Satellites

Jiannan Tu


The plasmasphere and high-latitude ionosphere/magnetosphere are two
important space environments around the Earth. This dissertation is
dedicated to advancing our understanding of the dynamics which determine the
plasma density distributions in the plasmasphere and high-latitude
ionosphere/magnetosphere.

We investigated effects of direct ion heating on field-aligned electron
density distributions in the plasmasphere using a field line
interhemispheric plasma (FLIP) model. It is found that direct ion heating in
the plasmasphere, possibly due to interactions of the plasmaspheric plasma
with energetic ring current ions, increases off-equatorial latitudinal
density gradients and is required to attain satisfactory agreement between
the simulated electron density profiles and those measured by the Radio
Plasma Imager (RPI) on the IMAGE satellite.

A dynamic fluid semi-kinetic (DyFK) model was utilized to model ion
field-aligned flow patterns observed by the Polar spacecraft over the
southern polar cap. The DyFK model was improved in the present study by
incorporating solutions of electron energy transport equations and by
implementing magnetic flux tube convection as specified by an empirical
ionospheric electric potential model. The effects of soft electron
precipitation, convection-driven frictional heating, centrifugal
acceleration, and wave-driven transverse ion heating are included in
simulations of ion flows within a flux tube drifting across the polar cap
from the cleft. The modeled evolution of O+ flow parameters at 5500 km
altitude exhibits patterns typical of those observed in connection with the
cleft ion fountain (CIF): upward O+ flows over the dayside cleft region,
downward flows within the central polar cap, and day-night ion density
asymmetries. It is shown that the day-night asymmetry of the O+ density
across the polar cap may be directly controlled by the CIF.

This improved DyFK model was also employed to simulate field-aligned
electron density profiles measured by IMAGE/RPI at polar latitudes.
Simulation results show that the measured electron density profiles may
consist primarily of contribution from O+ ions. The O+ dominance in the
simulated polar cap density profiles results from strong cleft ion fountain
effects. The simulated increase of O+ density can account for observed
electron density enhancement in the polar cap during this magnetic storm.

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Ph.D. Thesis, University of Alabama at Huntsville, 2004