Statistical study of ion flows in the dayside and nightside plasmasphere

Using the High Altitude Plasma Instrument (HAPI) on board the Dynamics Explorer 1 satellite, we have performed a statistical survey of ion flows which indicates possible inter-hemispheric flow of outer plasmaspheric ions from dayside sources to the nightside outer plasmasphere. The data were collected from the Northern Hemisphere during equinox and December solstice and during a period of solar maximum conditions. The analysis includes the study of approximately 40 dayside plasmaspheric passes and over 50 nightside passes covering a range of magnetic activity (0 < K_p < 7). The range of magnetic local times on the dayside is from about 6 to 12 h, while the nightside range is from about 18 to 23 h. Ion number fluxes, flow velocities, and temperatures are determined and binned as a function of invariant latitude. The results show a clear enhancement of outward dayside ion flows and nightside inward flows that were strongest during periods of maximum K_p index. The temperature of the ions decreased steadily equatorward into the outer plasmasphere. We have supplemented the HAPI results with data from the Retarding Ion Mass Spectrometer (RIMS) for a small subset of the statistical study. Six dayside and five nightside passes were examined in a similar manner using the RIMS data, which included ion fluxes in the range 0 < E < 50 eV. The results are in basic agreement with the HAPI data. Ion abundance ratios obtained from the Retarding Ion Mass Spectrometer indicate that the predominant ion species was H⁺, but relatively large densities of O⁺ were observed in the outer plasmasphere on several passes. We have traced the magnetic field from DE-1 altitudes in the dayside outer plasmasphere to conjugate positions sometimes in and usually near the nightside outer plasmasphere. Because strong eastward ion convection is observed in the nightside outer plasmasphere, we believe that a large dayside to nightside inter-hemispheric flow in the outer plasmasphere may take place during periods of increased magnetic activity along converting magnetic field lines.