DOWNWARD FLOWING IONS AND EVIDENCE FOR INJECTION OF IONOSPHERIC IONS INTO THE PLASMA SHEET

Energetic (keV) protons and 0** plus ions with field aligned pitch angle distributions and peak fluxes up to about 7 multiplied by 10**7 (cm**2 s sr keV)** minus **1 have been observed streaming downward in the high altitude (about 1 R//E ) auroral ionosphere. In two examples described in detail, the correlations observed between the downward flowing and coincident trapped ion populations suggest a common origin. Downward flowing ion events are a much less frequent phenomenon than upward flowing ion events in the auroral region. Spatially localized regions of enhanced hot plasma density were frequently observed in the low L portion of the plasma sheet. The results described suggest that upward flowing ions from the auroral acceleration regions are responsible for both the downward flowing ions and for at least some of the plasma clouds. A significant fraction of the equatorial substorm injected plasma clouds may thus result from this ionospheric source region.