Polar observations of topside field-aligned O+ flows and auroral forms

Measurements of thermal O+ ion densities, field-aligned velocities, and flu xes from the Thermal Ion Dynamics Experiment (TIDE) on Polar obtained near 5000 km altitude over the Southern Hemisphere are compared with auroral ima ges from the Ultraviolet Imager (UVI). Three passes were selected for analy sis in this paper based on data availability from the TIDE and UVI instrume nts. Results indicate upward O+ flows in the cleft region but downward O+ f lows in the polar cap region. Also, the O+ ion density follows a decreasing trend from the poleward side of the cusp region into the nightside. aurora region. The magnitude of the downward O+ parallel velocities increases fro m dayside to nightside across the polar cap boundary. The upflows tend to o ccur over or near auroral forms, while the downflows are seen in relatively dark regions, such as the polar cap. These results are consistent with a c left ion fountain source for the polar cap O+ ions. In the nightside polar cap, the results indicate a transition from downward to upflowing field-ali gned O+ ions near boundaries of bright auroral arcs.