Abstract
Since May 1977 the Ion Composition Experiments on board GEOS-1 and 2 have measured the abudance of magnetospheric ions in the energy per charge range from a few eV to 16 keV. Long term averages of a subset of this data, restricted to magnetic quiet (Kp ≦ 2) and the energy range 0.9 to 13.9 keV, reveal striking trends in magnetospheric ion composition over a period of nearly 3 years. These include a 10-fold increase in the average magnetospheric O +/H + ratio which is well correlated with increased solar activity as measured by the 10.7 cm solar radio flux. No comparable trend was found, for example, in the magnetospheric He ++/H + ratio which had an average value of (7.7 ±3.4) × 10 −.
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