The magnetosphere as a source of energetic magnetosheath ions

The dominant source of energetic ions upstream of the earth's bow shock remains controversial. Charge Composition Explorer (CCE) energetic (E > 10–15 keV) ion and magnetic field measurements near the spacecraft's 8.8 R E apogee during a period of greatly increased solar wind dynamic pressure on November 1, 1984 determine the sense of energetic ion streaming in the dayside magnetosphere, the magnetosheath, and the solar wind. The ions stream away from an appropriately compressed model magnetopause at all times in the magnetosheath and solar wind. The flux of energetic ions in the magnetosheath and solar wind rises to, but never exceeds, that in the magnetosphere. The observations are consistent with a magnetospheric, rather than a bow shock (Fermi acceleration) source for the ions in the magnetosheath during this event.