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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 29, issue 5
Ann. Geophys., 29, 931-944, 2011
https://doi.org/10.5194/angeo-29-931-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 29, 931-944, 2011
https://doi.org/10.5194/angeo-29-931-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 May 2011

30 May 2011

O+ heating associated with strong wave activity in the high altitude cusp and mantle

R. Slapak1, H. Nilsson1, M. Waara1, M. André2, G. Stenberg1, and I. A. Barghouthi3 R. Slapak et al.
  • 1Swedish Institute of Space Physics, Kiruna, Sweden
  • 2Swedish Institute of Space Physics, Uppsala, Sweden
  • 3Space Research Lab, Department of Physics, Al-Quds University, Jerusalem, Palestine

Abstract. We use the Cluster spacecraft to study three events with intense waves and energetic oxygen ions (O+) in the high altitude cusp and mantle. The ion energies considered are of the order 1000 eV and higher, observed above an altitude of 8 earth radii together with high wave power at the O+ gyrofrequency. We show that heating by waves can explain the observed high perpendicular energy of O+ ions, using a simple gyroresonance model and 25–45% of the observed wave spectral density at the gyrofrequency. This is in contrast to a recently published study where the wave intensity was too low to explain the observed high altitude ion energies. Long lasting cases (>10 min) of high perpendicular-to-parallel temperature ratios are sometimes associated with low wave activity, suggesting that high perpendicular-to-parallel temperature ratio is not a good indicator of local heating. Using multiple spacecraft, we show that the regions of enhanced wave activity are at least one order of magnitude larger than the gyroradius of the heated ions.

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