The magnetosphere as a sufficient source for upstream ions on November 1, 1984

Abstract

We consider 10 tests which distinguish the source of energetic particles in upstream ion events. Some tests are definitive, and others inadequate. In particular, we note that the Fermi model requires a finite time of magnetic field line connection to the bow shock before energetic ions appear and inverse velocity dispersion when the interplanetary magnetic field rotates to a more radial direction but that these features are also expected for the leakage model under certain conditions. We present simultaneous magnetospheric, magnetosheath, and upstream energetic particle observations during two well‐documented upstream events on November 1, 1984, and apply the 10 tests. The events are unusual in that they occurred during a period when the magnetosphere was greatly compressed, providing for an increase in the energetic magnetospheric particle population and a decrease in the magnetosheath thickness. Magnetospheric leakage satisfactorily explains our observations on this day, but in situ Fermi acceleration does not. Consequently, we consider magnetospheric leakage a sufficient source for upstream particles during these two events.