Charge states of substorm particle injections

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Abstract
The drift velocities of ions injected during substorms depend upon their energy and charge state. We use Medium Energy Particle Analyzer (MEPA) observations to time the arrival of peak proton, helium, and oxygen fluxes at the Charge Composition Explorer (CCE) satellite and determine the dominant ion charge states of these species in the energy range 72‐1000 KeV. The results indicate that freshly‐injected helium (72‐240 KeV) and oxygen (137‐365 KeV) are singly‐ionized, but that more energetic oxygen (>365 KeV) is multiply‐charged. This suggests either a dominant ionospheric source at the lower energies and a solar wind source at the higher energies or an energization of the pre‐existing ring current population.