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

Abstract

Investigations of the average spatial distributions of the ionospheric ions O + and O 2+ and of the solar wind ions O 6+ and C 6+ 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 O 2+ ions have radial profiles with maxima at about L = 5 and diurnal variations with a broad maximum on the dayside. The O 6+ and C 6+ ion fluxes increase with L between L = 5 and L = 7 and level off farther out. The diurnal variations of the relative O 6+ and C 6+ 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 O 2+ fluxes as well as the minimum of the O 6+ and C 6+ fluxes on the dayside can be explained by drift shell splitting. The inward transport is associated with ion losses, mainly by charge exchange. O 6+ and C 6+ ions are removed already at larger distances than O + and O 2+ . 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).