Simulation of polar cap field-aligned electron density profiles measured with 
the IMAGE radio plasma imager

J.-N. Tu, J. L. Horwitz, P. A. Nsumei, P. Song, X.-Q. Huang, B. W. Reinisch


The radio plasma imager (RPI) on board the IMAGE satellite measured a set of
field-aligned electron density profiles at polar latitudes during a weak
magnetic storm on 4 March 2003. Several of those density profiles as well as a
density profile measured under moderately quiet conditions are compared with
those simulated by a dynamic fluid semikinetic (DyFK) model. In this DyFK model,
the collision-dominated portion of the flux tube is treated with a moment-based
fluid model for altitudes from 120 to 1100 km, while the generalized semikinetic
model is used for the 800 km to 3 R E region. The effects of auroral soft
electron precipitation, convection-driven frictional ion heating, centrifugal
acceleration, and wave-driven transverse ion heating are incorporated into
simulations of ion field-aligned flows within flux tubes drifting along
empirical model specified convection trajectories across the polar ionosphere.
It is found that using reasonable parameters for the indicated energization
processes allows agreement between the modeled field-aligned electron density
profiles and those measured by IMAGE/RPI. The simulation results suggest that
for the cases considered, the IMAGE/RPI measured electron density profiles may
consist primarily of contributions from O+ ions. The O+ dominance in the
simulated polar cap density profiles resulted from cleft ion fountain effects.
The simulated enhancement of the O+ density accounts for the electron density
enhancement in the polar cap during the magnetic storm.

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Journal of Geophysical Research, 109, A07206, doi:10.1029/2003JA010310, 2004