Determining the Mass Composition of the Plasmasphere using
Ground-Based Techniques and IMAGE RPI: A Statistical Study

David Berube, Mark Moldwin, Gemin Keshishian
UCLA Institute of Geophysics and Planetary Physics

Shing Fung, James Green
NASA Goddard Space Flight Center, Greenbelt, MD


The average plasma mass density profile of the inner magnetosphere
from 1.74 < L < 3.12 has been determined by compiling over 5200
hours of equatorial mass density computations using data from the
MEASURE chain of ground-based magnetometers. The average ion
mass as a function of L-shell is also computed by comparison with
the equatorial electron density profile from IMAGE RPI. The average
ion mass is used to constrain the overall concentration of heavy ions
for different levels of geomagnetic activity. In particular, we find
that during disturbed times, the concentration of heavy ions
increases with increasing L-shell. At L=3, for the most disturbed
times, we find a maximum O+ concentration of approximately 30
percent, and a minimum of ~13 percent if we assume a purely He+
and O + plasma.

_______________
GEM 2003 Summer Workshop, Snowmass, CO, June 22-27, 2003