HIGH-LATITUDE FIELD-ALIGNED LIGHT-ION FLOWS IN THE TOPSIDE IONOSPHEREDEDUCED FROM ION COMPOSITION AND PLASMA TEMPERATURES

Under the assumption of steady state conditions, the continuity and mo mentum equations can be solved locally for magnetic field aligned ion flow velocities given the local ion concentrations, electron and ion t emperatures and their vertical gradients, as well as the neutral compo sition derived from the MSIS model. Using a comprehensive ionospheric data set comprised of all available ion composition and plasma tempera ture measurements from satellites, the vertical distributions of ion c omposition and plasma temperatures are defined from middle latitudes u p into the polar cap for summer conditions for altitudes below approxi mately 1200 km. These data are sufficient to allow a numerical estimat ion of the latitudinal variation of the light ion outflows from within the plasmasphere to the polar wind regions. The altitude at which sig nificant light ion outflow begins is found to be lower during solar mi nimum conditions than during solar maximum. The H+ outward speeds are of the order of 1 km/s near 1100 km (the limit of the observations) du ring solar maximum but attain several km/s speeds for solar minimum. H e+ shows a similar altitude development of flow but attains polar cap speeds much less than 1 km/s at altitudes below 1100 km, particularly under solar maximum conditions. Outward flows are also found in the to pside F-region for noontime magnetic flux tubes within the plasmaspher e.