A Simple Approach to Reproducing IMAGE/RPI-Derived Field-Aligned Electron 
Density Profiles During Plasmaspheric Refilling

Phillip A. Webb
NASA Goddard Space Flight Center 
Greenbelt, Maryland 20771

Bodo W. Reinisch, Xueqin Huang
University of Massachusetts at Lowell
Lowell, Massachusetts 01854

M. Anthony Reynolds
Embry-Riddle University
Daytona Beach, Florida 32114

Robert F. Benson, James L. Green
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771


Magnetic field-aligned electron-density (Ne) profiles can be calculated 
from active soundings using the Radio Plasma Imager (RPI) on the Imager 
for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite. By 
observing these profiles under different geomagnetic conditions, the 
underlying physics that control the Ne distribution can be investigated.

In this presentation RPI observations will be used to show that a magnetic 
field line depleted of plasma has an Ne distribution approximating a 
collisionless (CL) profile, while a saturated field line has a diffusive 
equilibrium (DE) profile.  Furthermore, by using the RPI-derived profiles 
it is possible to observe the transition from the depleted CL profile to 
the saturated DE profile. Using computationally simple CL and DE models as 
upper and lower boundaries respectively, methods to vary the distribution 
between these two extremes that reproduces the refilling of the 
field-aligned Ne profiles observed by RPI will be presented. Furthermore, 
the results of this approach will be compared with the Multi-Species 
Kinetic Plasmasphere Model (MSKPM), a kinetic field-aligned model that 
simulates the plasmaspheric refilling by single particles from the 
underlying exosphere.

Comparisons of the Global Plasmasphere Ionosphere Density (GPID) model 
with IMAGE Ne observations from passive and active RPI operations will 
demonstrate the increased accuracy of GPID when the improved CL-DE 
field-aligned Ne distribution is included in the model.

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002