HIGH CHARGE-STATE CARBON AND OXYGEN IONS IN EARTHS EQUATORIAL QUASI-TRAPPING REGION

Observations of energetic (1.5 - 300 keV/e) medium-to-high charge state (+3 less-than-or-equal-to Q less-than-or-equal-to +7) solar wind origin C and O ions made in the quasi-trapping region (QTR) of Earth's magnetosphere are compared to ion trajectories calculated in model equatorial mapetospheric magnetic and electric fields.. These comparisons indicate that solar wind ions entering the QTR on the nightside as an energetic component of the plasma sheet exit the region on the dayside, experiencing little or no charge exchange on the way. Measurements made by the CHarge Energy Mass (CHEM) ion spectrometer on board the AMPTE/CCE spacecraft at 7 < L < 9 from September 1984 to January 1989 are the source of the new results contained herein: quantitative long-term determination of number densities, average energies, energy spectra, local time distributions, and their variation with geomagnetic disturbance level as indexed by Kp. Solar wind primaries (ions with charge states unchanged) and their secondaries (ions with generally lower charge states produced from primaries in the magnetosphere via charge exchange) are observed throughout the QTR and have distinctly different local time variations that persist over the entire 4-year analysis interval. During Kp greater-than-or-equal-to 3(o) intervals, primary ion (e.g., O+6) densities exhibit a pronounced predawn maximum with average energy minimum and a broad near-local-noon density minimum with average energy maximum. Secondary ion (e.g., O+5) densities do not have an identifiable predawn peak, rather they have a broad dayside maximum peaked in local morning and a nightside minimum. During Kp less-than-or-equal-to 2- intervals, primary ion density peaks are less intense, broader in local time extent, and centered neu midnight, while secondary ion density local time variations diminish. The long-time-interval baseline helps to refine and extend previous observations; for example, we show that ionospheric contribution to O+3 is negligible. Through comparison with model ion trajectories, we interpret the lack of pronounced secondary ion density peaks colocated with the primary density peaks to indicate that: (1) negligible charge exchange occurs at L > 7, that is, solar wind secondaries are produced at L < 7, and (2) solar wind secondaries do not form a significant portion of the plasma sheet population injected into the QTR. We conclude that little of the energetic solar wind secondary ion population is recirculated through the magnetosphere.