EISCAT CRRES OBSERVATIONS - NIGHTSIDE IONOSPHERIC ION OUTFLOW AND OXYGEN-RICH SUBSTORM INJECTIONS/

We present combined observations made near midnight by the EISCAT rada r, all-sky cameras and the combined released and radiation efects sate llite (CRRES) shortly before and during a substorm. In particular, we study a discrete, equatorward-drifting auroral are, seen several degre es poleward of the onset region. The are passes through the field-alig ned beam of the EISCAT radar and is seen to be associated with a consi derable upflow of ionospheric plasma. During the substorm, the CRRES s atellite observed two major injections, 17 min apart, the second of wh ich was dominated by O+ ions. We show that the observed are was in a s uitable location in both latitude and MLT to have fed O+ ions into the second injection and that the upward flux of ions associated with it was sufficient to explain the observed injection. We interpret these d ata as showing that arcs in the nightside plasma-sheet boundary layer could be the source of O+ ions energised by a dipolarisation of the mi d- and near-Earth tail, as opposed to ions ejected from the dayside io nosphere in the cleft ion fountain.