CRRES observations of stormtime ring current ion composition

The Magnetospheric Ion Composition Spectrometer onboard the CRRES spacecraft provided mass and charge state composition data for positive ions in the energy-per-charge range 1-426 keV/e. The CRRES data is compared to the AMPTE/CCE observations during a moderately large geomagnetic storm on 4 June 1991. The results are compared to observations of large storms by CRRES and by the AMPTE/CCE spacecraft. The CRRES data show that oxygen ions formed 29% of the total measured ion energy density at L = 3-5 during the storm recovery phase. This result implies that domination of the plasma by oxygen ions may not be necessary to produce the observed rapid initial recovery of the Dst magnetic index. A preliminary test of the Dessler-Parker-Sckopke relation between the ion energy and the global magnetic perturbation shows that the observed particle fluxes during the 4 June 1991 storm could account for only 40-70% of the variation of Dst.