Latitudinal Density Dependence Along Geomagnetic Field Lines

Goldstein, J., Denton, R.E., Hudson, M.K., Miftakhova, E., Menietti, J.D., Gallagher, D.,  
Reiff, P.H.

Using observations of the electron density n{e} based on measurement of the upper hybrid
resonance frequency by the Polar spacecraft Plasma Wave Instrument (PWI), we have examined
the radial density dependence along field lines in the outer plasmasphere and the near
plasmatrough. Sampled L values range from 2.5 to 6.6. Our technique depends on the fact that
Polar crosses particular L values at two different points with different radial distance R. 
In our plasmaspheric data set (n{e} > 100 cm(-1)), we find that on average n{e} is flat along 
field lines from the equator up to the latitudes sampled by Polar (R < 2.0). In the
plasmatrough data set (n{e} < 100 cm(-1), there is on average a mild radial dependence 
n{e} proportional to R^{-1.7}. The IMAGE spacecraft will fly in a (similar) elliptical polar
orbit with an apogee at 7 RE, and will carry the Radio Plasma Imager (RPI), allowing the
observation of radar echos from global plasma structures. The expected data from RPI will be 
part of the continuing investigation of the radial density dependence of 
magnetospheric/plasmaspheric field lines. 

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Presented at the Spring American Geophysical Union Meeting, 
Washington, D.C., May 30-June 3, 2000