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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 29, issue 6
Ann. Geophys., 29, 1049-1060, 2011
https://doi.org/10.5194/angeo-29-1049-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Cluster 10th anniversary workshop

Ann. Geophys., 29, 1049-1060, 2011
https://doi.org/10.5194/angeo-29-1049-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  16 Jun 2011

16 Jun 2011

Cluster observations of trapped ions interacting with magnetosheath mirror modes

J. Soucek1,2 and C. P. Escoubet1 J. Soucek and C. P. Escoubet
  • 1ESTEC, European Space Agency, Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
  • 2Institute of Atmospheric Physics, Bocni II 1401, 141 31 Prague, Czech Republic

Abstract. Mirror modes are among the most intense low frequency plasma wave phenomena observed in the magnetosheaths of magnetized planets. They appear as large amplitude non-propagating fluctuations in the magnetic field magnitude and plasma density. These structures are widely accepted to represent a non-linear stage of the mirror instability, dominant in plasmas with large ion beta and a significant ion temperature anisotropy T/T>1. It has long been recognized that the mirror instability both in the linear and non-linear stage is a kinetic process and that the behavior of resonant particles at small parallel velocities is crucial for its development and saturation. While the dynamics of the instability and the effect of trapped particles have been studied extensively in theoretical models and numerical simulations, only spurious observations of the trapped ions were published to date. In this work we used data from the Cluster spacecraft to perform the first detailed experimental study of ion velocity distribution associated with mirror mode oscillations. We show a conclusive evidence for the predicted cooling of resonant ions at small parallel velocities and heating of trapped ions at intermediate pitch angles.

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