Characterizing the mass composition of the inner magnetosphere using ground 
and space-based techniques

D. Berube, M. Moldwin, S. Fung, J. Green

Electron number density measurements from IMAGE RPI are combined with ULF
resonance-ground magnetometer derived mass density estimates during times of
IMAGE and MEASURE ground magnetometer array conjunctions to determine the
average composition of the plasmasphere during quiet times.  Many studies 
have been performed to characterize the plasma density profile of the inner
magnetosphere.  The usual result is that the equatorial electron density
decreases as a function of distance from the Earth.  On the other hand, the
mass density profile of the inner magnetosphere has not been extensively
studied due to the difficulty of making direct measurements from spacecraft
and the fact that ground-based techniques developed for remotely sensing mass
density tend to be tedious to perform by hand.  Recently, an automated process
for estimating the mass density of the inner magnetosphere using pairs of
ground magnetometers has been developed by Berube et al.  The Radio Plasma
Imager (RPI) on board the IMAGE spacecraft makes in situ measurements of
magnetospheric electron density.  By combining electron density measurements
from RPI with mass density estimates obtained using ground techniques we are
able to constrain the plasma composition of the inner magnetosphere for
instances when IMAGE is in conjunction with the field lines spanned by ground
stations.

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Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003