Journal cover Journal topic
Annales Geophysicae Sun, Earth, planets, and planetary systems An interactive open-access journal of the European Geosciences Union
Ann. Geophys., 28, 907-916, 2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.
08 Apr 2010
Oxygen ion energization observed at high altitudes
M. Waara1, H. Nilsson1, G. Stenberg1, M. André2, H. Gunell3, and H. Rème4 1Swedish Institute of Space Physics, Kiruna, Sweden
2Swedish Institute of Space Physics, Uppsala, Sweden
3West Virginia University, Morgantown, USA
4CESR, Toulouse, France
Abstract. We present a case study of significant heating (up to 8 keV) perpendicular to the geomagnetic field of outflowing oxygen ions at high altitude (12 RE) above the polar cap. The shape of the distribution functions indicates that most of the heating occurs locally (within 0.2–0.4 RE in altitude). This is a clear example of local ion energization at much higher altitude than usually reported. In contrast to many events at lower altitudes, it is not likely that the locally observed wave fields can cause the observed ion energization. Also, it is not likely that the ions have drifted from some nearby energization region to the point of observation. This suggests that additional fundamentally different ion energization mechanisms are present at high altitudes. One possibility is that the magnetic moment of the ions is not conserved, resulting in slower outflow velocities and longer time for ion energization.

Citation: Waara, M., Nilsson, H., Stenberg, G., André, M., Gunell, H., and Rème, H.: Oxygen ion energization observed at high altitudes, Ann. Geophys., 28, 907-916,, 2010.
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