Observations of the flow of H+ and He+ along magnetic field lines in the plasmasphere

Abstract

The dynamics of earth's plasmasphere is affected by gradients in the plasma pressure, the convection electric field, and the corotation electric field. The Retarding Ion Mass Spectrometer (RIMS) on Dynamics Explorer 1 measures the pitch angles of this plasma from which the total plasma velocity vector can be determined. Using assumptions concerning the relative importance of convection and corotation, the velocity of ions along the magnetic field line can be determined. These results represent the first direct observations of ion velocities along magnetic field lines at high altitudes in the plasmasphere. Data from October 1981 through January 1982 have revealed several interesting aspects of the field‐aligned flow of H+ and He+. Downward directed velocities observed in the northern hemisphere within 30° of the equatorial plane are interpreted as interhemispheric flows. Typical velocities are of the order of a few hundred meters per second. Higher‐speed (up to 1 km s−1) flows observed in the outer plasmasphere appear to be associated with refilling. Counterstreaming of H+ and He+ has been observed in the autumn and winter hemisphere with He+ flowing upward and H+ flowing downward. Differences between these results and theoretical work can probably be attributed to differences in the season and the density level within the flux tube.