Statistics of high-altitude and high-latitude O⁺ ion outflows observed by Cluster/CIS

Abstract. The persistent outflows of O⁺ ions observed by the Cluster CIS/CODIF instrument were studied statistically in the high-altitude (from 3 up to 11 R_E) and high-latitude (from 70 to ~90 deg invariant latitude, ILAT) polar region. The principal results are: (1) Outflowing O⁺ ions with more than 1keV are observed above 10 R_E geocentric distance and above 85deg ILAT location; (2) at 6-8 R_E geocentric distance, the latitudinal distribution of O⁺ ion outflow is consistent with velocity filter dispersion from a source equatorward and below the spacecraft (e.g. the cusp/cleft); (3) however, at 8-12 R_E geocentric distance the distribution of O⁺ outflows cannot be explained by velocity filter only. The results suggest that additional energization or acceleration processes for outflowing O⁺ ions occur at high altitudes and high latitudes in the dayside polar region.

Keywords. Magnetospheric physics (Magnetospheric configuration and dynamics, Solar wind-magnetosphere interactions)