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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, 945–954, 2011
https://doi.org/10.5194/angeo-29-945-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 29, 945–954, 2011
https://doi.org/10.5194/angeo-29-945-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 May 2011

30 May 2011

Statistical evidence for O+ energization and outflow caused by wave-particle interaction in the high altitude cusp and mantle

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

Abstract. We present a statistical study of the low (<1 Hz) frequency electric and magnetic field spectral densities observed by Cluster spacecraft in the high altitude cusp and mantle region. At the O+ gyrofrequency (0.02–0.5 Hz) for this region the electric field spectral density is on average 0.2–2.2 (mV m−1)2 Hz−1, implying that resonant heating at the gyrofrequency can be intense enough to explain the observed O+ energies of 20–1400 eV. The relation between the electric and magnetic field spectral densities results in a large span of phase velocities, from a few hundred km s−1 up to a few thousand km s−1. In spite of the large span of phase velocity, the ratio between the calculated local Alfvén velocity and the estimated phase velocity is close to unity. We provide average values of a coefficient describing diffusion in ion velocity space at different altitudes, which can be used in studies of ion energization and outflow. The observed average waves can explain the average O+ energies measured in the high altitude (8–15 RE) cusp/mantle region of the terrestrial magnetosphere according to our test particle calculations.

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