Plasma characteristics of upflowing ion beams in the polar cap region

The plasma characteristic of O+, H+ and He+ beam events in the polar cap region observed near solar maximum by the Dynamics Explorer 1 (DE 1) satellite are analyzed in this paper. The data analyzed were taken from both the energetic ion composition spectrometer (EICS), and the ion mass spectrometer (RIMS). Electron densities measured by the plasma wave instrument (PWI) provided limits on estimates of ion densities. A subset of upflowing polar cap ion streams was identified from which it was possible to make estimates of the plasma characteristics using the three DE 1 instruments described above. In this paper, the data for two polar ion streams are presented in detail. The plasma was found to consist of multiple streaming and quasi-isotropic components. In both cases, estimates of temperatures and densities were made taking into account possible spacecraft potentials. The ion densities of several other events were also estimated. It was found that (1) the plasma often had a large content of upflowing O+ ions, (2) there was a significant amount of O+ in the plasma even during quiet auroral conditions when the AE index was only 37 nT, (3) in one event presented, the upflowing O+ population had both a cold and a warm field-aligned distribution, (4) in another event presented, the O+ and H+ temperatures were estimated to be 5 eV and 7.6 eV, respectively, suggesting that the ionospheric ions were heated, and (5) the cold upflowing ion stream component observed in some of the polar ion streaming events exhibited a filamentary nature