The helium components of energetic terrestrial ion upflows: Their occurrence, morphology, and intensity

A statistical survey of the occurrence of upflowing He+ seen by the energetic ion mass spectrometer on Dynamics Explorer −1 above the high‐latitude ionosphere shows that the spatial and temporal distribution of upflowing He+ in the 10‐eV to 17‐keV energy range follows a pattern which is broadly similar to those of H+ and O+ in this energy range. It also shows that energetic He+ is a minor part of the high‐latitude ion outflow. Upflowing He+ is detected only half as often as either H+ or O+, and typically the intensities of upflowing He+ are much less than those of H+ or O+. However, the intensity of the He+ outflow quite often reaches the maximum outflow of cool He+ predicted by steady state ionospheric models and occasionally reaches substantially higher levels. This suggests that probably much of the time the major part of the outflowing ionospheric plasma is accelerated to energies of at least 10 eV and that there may be additional, non‐steady state processes which can sometimes extract unusually large amounts of ionospheric He+.