The Inner Magnetosphere Empirical Plasma Density Model Based on Radio Plasma 
Imager Observations

B. Reinisch (1), X. Huang (1), P. Song (1), P. Nsumei (1), J. Green (2), and  
D. Gallagher (3)

(1) Environmental, Earth, and Atmospheric Sciences Department., Center for 
    Atmospheric Research, University of Massachusetts Lowell, MA 01854, 
(2) NASA Goddard Space Flight Center, Greenbelt, MD  20771 
(3) NASA Marshal Space Flight Center, Huntsville, AL 35805


A new Inner Magnetosphere Empirical Plasma density distribution model (IMEP) is 
being developed using the radio plasma imager (RPI) measurements on the IMAGE 
satellite. RPI performs radio sounding in the magnetosphere using frequencies 
between 3 kHz and 3 MHz. IMAGE is on an elliptical polar orbit with an apogee 
altitude of 7.4 RE, and a perigee of 1,400 km. The recorded plasmagrams show 
echo traces that are formed by signals propagating over distances of up to 7 RE. 
In many instances these signals propagate along the magnetic field. A newly 
developed technique inverts the echo traces on the plasmagrams to electron 
density profiles along the field lines. By using consecutive profiles measured 
at varying L shells while IMAGE orbits through the plasmapause into the 
plasmasphere, it becomes possible to develop an empirical plasmasphere density 
model. Our results show a symmetric plasmasphere density distribution around the 
magnetic equator at equinox, while higher densities are contained in the winter 
hemisphere during solstice. When IMAGE is in the polar cap region, the vertical 
polar cap plasma density distribution is determined. Our results show the 
density varying with distance as R-5 in the polar cap, and to increase 
exponentially with magnetic activity. Once fully developed, IMEP could be 
considered a magnetospheric extension of the IRI model.

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Presented at the 34th COSPAR Scientific Assembly, Houston, Texas, U.S.A.  
10-19 October 2002