The Oxygen Ion Circulation in The Outer Terrestrial Magnetosphere and Its Dependence on Geomagnetic Activity

Abstract

We have quantified the O⁺ transports in the plasma sheet and lobes (-20 < X_GSM<-10R_E) and their dependencies on geomagnetic activity, Kp, using Cluster data. We found that they have similar behavior as the polar region O⁺ outflow as well as the O⁺ fluxes in the plasma mantle and high-latitude dayside magnetosheath, in their response to geomagnetic activity. The sum of the total O⁺ fluxes in the lobes, plasma sheet, plasma mantle, and high-latitude magnetosheath equals the O⁺ outflow above the polar regions for any geomagnetic condition. It can be argued that there are no hidden O⁺ populations for Cluster, in the sense that there are no significant amounts of O⁺ with energies outside the energy range of the ion spectrometer, Composition Distribution Function, and/or below the spacecraft potential. Therefore, we have obtained a complete picture of the O⁺ circulation (and escape) in the outer magnetosphere and its dependence on geomagnetic activity.