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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 27, issue 2
Ann. Geophys., 27, 601–615, 2009
https://doi.org/10.5194/angeo-27-601-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 601–615, 2009
https://doi.org/10.5194/angeo-27-601-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  06 Feb 2009

06 Feb 2009

Mirror structures above and below the linear instability threshold: Cluster observations, fluid model and hybrid simulations

V. Génot1, E. Budnik2, P. Hellinger3, T. Passot4, G. Belmont5, P. M. Trávníček3, P.-L. Sulem4, E. Lucek6, and I. Dandouras1 V. Génot et al.
  • 1CESR, Université de Toulouse (UPS) & CNRS (UMR5187), Toulouse, France
  • 2Noveltis, 2 Avenue de l'Europe, 31520 Ramonville Saint-Agne, France
  • 3Institute of Atmospheric Physics and Astronomical Institute, AS CR, Prague, Czech Republic
  • 4CNRS, Observatoire de la Côte d'Azur, Nice, France
  • 5CETP-CNRS, Vélizy, France
  • 6Space and Atmospheric Physics Group, Blackett Laboratory, Imperial College, London, UK

Abstract. Using 5 years of Cluster data, we present a detailed statistical analysis of magnetic fluctuations associated with mirror structures in the magnetosheath. We especially focus on the shape of these fluctuations which, in addition to quasi-sinusoidal forms, also display deep holes and high peaks. The occurrence frequency and the most probable location of the various types of structures is discussed, together with their relation to local plasma parameters. While these properties have previously been correlated to the β of the plasma, we emphasize here the influence of the distance to the linear mirror instability threshold. This enables us to interpret the observations of mirror structures in a stable plasma in terms of bistability and subcritical bifurcation. The data analysis is supplemented by the prediction of a quasi-static anisotropic MHD model and hybrid numerical simulations in an expanding box aimed at mimicking the magnetosheath plasma. This leads us to suggest a scenario for the formation and evolution of mirror structures.

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