Mapping of the heavy ion outflows as seen by IMAGE and multifluid global modeling for the 17 April 2002 storm

Multifluid global modeling that includes both light and heavy ion dynamics is used to investigate changes in magnetospheric dynamics produced by enhanced ionospheric outflows for the 17 April 2002 storm. The predicted outflow rates and their effects on the magnetosphere are compared with AMIE and IMAGE/HENA data as a function of relative O+ concentration in the ionosphere. It is shown that O+ can be the dominant species on the dusk side in the inner magnetosphere during the periods of high activity even for ionospheric concentrations as low as 5% as a result of differential heavy ion convection patterns. However, for these low outflow conditions, the cross-polar cap potential is much larger than that calculated by AMIE. As the O+ ionospheric concentration increases, the heavy outflow rate approaches canonical values, and the effective ionospheric resistivity falls in association with a decrease in cross-polar cap potential and an increase in the auroral field aligned currents. Within the magnetosphere, the region where the O+ concentration exceeds 50% expands toward the duskside and down the tail. Pressures in excess of 1 nPa can be supported by the enhanced O+ outflows. The presence of these enhanced outflows appears at about the same time and over a similar region to enhancements seen in the HENA 51-180 keV oxygen data. These results provide a direct tie between heavy ionospheric outflows and their energization in the tail and suggest that during this period the heavy ions provide a substantial amount of the plasma required to support the magnetotail current sheet. The model results also show that the enhanced O+ outflow leads to the enhanced exclusion of light ions of both solar wind and ionospheric origin in the plasma sheet, albeit with the light ions experiencing enhanced heating in an O+ dominated current sheet. These results indicate that observed heavy ionospheric outflows and their energetization in the tail have global consequences for the magnetosphere including supporting the dynamics of the tail current sheet during active times and in global circulation including the cross-polar cap potential and the region 1 and 2 currents.