Simultaneous observations of H+ and O+; ions at two altitudes by the Akebono and Dynamics Explorer 1 satellites

Abstract

We report simultaneous observations of H+ and O+ ions from the suprathermal ion mass spectrometer (SMS) on Akebono and the energetic ion composition spectrometer (EICS) on Dynamics Explorer 1. These observations were made simultaneously above and below regions of ion acceleration on auroral and polar cap magnetic field lines. The evening auroral zone data reported here directly confirm the existence of an ionospheric preenergization mechanism for oxygen ions. The preenergized oxygen ions have characteristic energies of the order of 10 eV and are transported to altitudes of several thousand kilometers where they acquire significant additional energy. Nearly simultaneous observations of O+ ions on polar cap field lines near the cusp/cleft region reveal two distinct populations. The first population is energized at altitudes of a few thousand kilometers and transported up and into the polar cap by the combination of the effects of the gradient in the magnetic field and the prevailing magnetospheric convection field. The second population has significantly more energy than the first. This second population could arise through several mechanisms, which are identified and discussed. The data presented illustrate that the creation (energization) and transport of streams of upflowing ions in the polar cap is more complex than previously anticipated and point to the importance and our limited knowledge of ionospheric processes responsible for the pre‐energization of oxygen ions.