Average spatial distributions of energetic O+, O2+, O6+, and C6+ ions in the magnetosphere observed by AMPTE CCE

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Abstract
Investigations of the average spatial distributions of the ionospheric ions O+ and O2+ and of the solar wind ions O6+ and C6+ provide a possibility to estimate the relative contributions of the ionosphere and the solar wind to the energetic ion population in the magnetosphere. We used measurements with the charge energy mass spectrometer (CHEM) on board the AMPTE CCE spacecraft to determine the relative fluxes of these ions near the equatorial plane as a function of the drift shell parameter L, the magnetic activity index Kp, and the local time LT. The O+ and O2+ ions have radial profiles with maxima at about L = 5 and diurnal variations with a broad maximum on the dayside. The O6+ and C6+ ion fluxes increase with L between L = 5 and L = 7 and level off farther out. The diurnal variations of the relative O6+ and C6+ fluxes exhibit a pronounced minimum on the dayside. The observations can be interpreted in terms of ion convection from the tail onto quasi‐trapped drift orbits and further radial diffusion onto closed drift shells. The maximum of the O+ and O2+ fluxes as well as the minimum of the O6+ and C6+ fluxes on the dayside can be explained by drift shell splitting. The inward transport is associated with ion losses, mainly by charge exchange. O6+ and C6+ ions are removed already at larger distances than O+ and O2+. As a result, the ionosphere contributes most of the oxygen ions in the magnetosphere. Important contributions from the solar wind are encountered in the outer magnetosphere (L > 7).