Polar wind survey with the Thermal Ion Dynamics Experiment Plasma Source Instrument suite aboard POLAR

In February 1996, the POLAR spacecraft was placed in an elliptical orbit wi th a 9 R-E geocentric distance apogee in the northern hemisphere and 1.8 R- E perigee in the southern hemisphere. The Thermal Ion Dynamics Experiment ( TIDE) on POLAR has allowed sampling of the three-dimensional ion distributi on functions with excellent energy, angular, and mass resolution. The Plasm a Source Instrument (PSI), when operated, allows sufficient diminution of t he electric potential to observe the polar wind at very high altitudes. In this paper, we describe the results of a survey of the polar wind character istics for H+, He+, and O+ as observed by TIDE at similar to 5000 km and si milar to 8 R-E altitudes over the polar cap during April-May 1996. At 5000 km altitude, the H+ polar wind exhibits a supersonic outflow, while O+ show s subsonic downflow, which suggests a cleft ion fountain origin for the Oions in the polar cap region. Dramatic decreases of the 5000 km altitude H and O+ ion densities and fluxes are seen as the solar zenith angle increas es from 90 degrees to 100 degrees for the ionospheric base, which is consis tent with solar illumination ionization control. However, the polar cap dow nward O+ flow and density decline from dayside to nightside in magnetic coo rdinates suggest a cleft ion fountain origin for the polar cap O+. Cleft io n fountain origin O+ density plumes could also be partially responsible for a similar day-night asymmetry in H+ owing to the charge-exchange reaction. At 8 R-E altitude, both H+ and O+ outflows are supersonic and H+ is the hi ghly dominant ion species. The average bulk ion field-aligned velocities ar e in the typical ratio VO+ : VHe+: VH+ similar to 2 : 3 : 5, which may sugg est a tendency toward comparable energy gains, such as via an electric pote ntial layer.