POLAR CAMMICE Observations of Ion Injection and Transport in the High-latitude Magnetosphere

Dr. Tim Stubbs
Imperial College
United Kingdom

We infer the injection and transport of ions about the convection-dominated region of the Earth's magnetosphere from observations made by the CAMMICE Magnetospheric Ion Composition Sensor (MICS) aboard the Polar spacecraft. We plot the occurrence probability of ion species as a function of invariant latitude and magnetic local time. We first survey He++ ions, as they can be used as a tracer of ions of solar wind origin within the magnetosphere. For E/q values from 1 to 10 keV/e enhancements are observed near local noon and along the dawn flank. The former is identified as the cusp, while the latter dawn-dusk asymmetry is due to the drift orbits of ions convecting earthward from the tail, and not from direct entry via the mechanisms tested. In the tail, ions ExB drift toward dawn and gradient/curvature drift toward dusk. When we observe ions at higher energies, we see the asymmetry flip to the dusk flank as the gradient/curvature drift dominates. We similarly survey the total ion signature measured by MICS and compare it with the survey by Newell and Meng (1992) of magnetospheric particle precipitation into the ionosphere as observed the DMSP spacecraft. Finally, we test the drift orbit hypothesis by quantifying the "crossover" energy at which the ExB and gradient/curvature drifts are equal and opposite. These crossover energies are compared with a simple analytical model and are shown to vary with the sense of the IMF Bz component and, therefore, the strength of the cross-tail convection electric field, as expected.