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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 9
Ann. Geophys., 26, 2899–2910, 2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: STAMMS: Spatio-Temporal Analysis and Multipoint Measurements...

Ann. Geophys., 26, 2899–2910, 2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Sep 2008

23 Sep 2008

On nonstationarity and rippling of the quasiperpendicular zone of the Earth bow shock: Cluster observations

V. V. Lobzin1,*, V. V. Krasnoselskikh1, K. Musatenko1, and T. Dudok de Wit1 V. V. Lobzin et al.
  • 1LPCE/CNRS-Université d'Orléans, Orleans, France
  • *now at: the University of Sydney, Sydney, Australia

Abstract. A new method for remote sensing of the quasiperpendicular part of the bow shock surface is presented. The method is based on analysis of high frequency electric field fluctuations corresponding to Langmuir, upshifted, and downshifted oscillations in the electron foreshock. Langmuir waves usually have maximum intensity at the upstream boundary of this region. All these waves are generated by energetic electrons accelerated by quasiperpendicular zone of the shock front. Nonstationary behavior of the shock, in particular due to rippling, should result in modulation of energetic electron fluxes, thereby giving rise to variations of Langmuir waves intensity. For upshifted and downshifted oscillations, the variations of both intensity and central frequency can be observed. For the present study, WHISPER measurements of electric field spectra obtained aboard Cluster spacecraft are used to choose 48 crossings of the electron foreshock boundary with dominating Langmuir waves and to perform for the first time a statistical analysis of nonstationary behavior of quasiperpendicular zone of the Earth's bow shock. Analysis of hidden periodicities in plasma wave energy reveals shock front nonstationarity in the frequency range 0.33 fBi<f<fBi, where fBi is the proton gyrofrequency upstream of the shock, and shows that the probability to observe such a nonstationarity increases with Mach number. The profiles observed aboard different spacecraft and the dominating frequencies of the periodicities are usually different. Hence nonstationarity and/or rippling seem to be rather irregular both in space and time rather than resembling a quasiregular wave propagating on the shock surface.

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