Articles | Volume 28, issue 4
Ann. Geophys., 28, 907–916, 2010
https://doi.org/10.5194/angeo-28-907-2010
Ann. Geophys., 28, 907–916, 2010
https://doi.org/10.5194/angeo-28-907-2010

  08 Apr 2010

08 Apr 2010

Oxygen ion energization observed at high altitudes

M. Waara1, H. Nilsson1, G. Stenberg1, M. André2, H. Gunell3, and H. Rème4 M. Waara et al.
  • 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.

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