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Ann. Geophys., 22, 2283-2288, 2004
www.ann-geophys.net/22/2283/2004/
© European Geosciences Union 2004
Magnetic turbulent spectra in the magnetosheath: new insights
F. Sahraoui1, G. Belmont1, J. L. Pinçon2, L. Rezeau1,3, A. Balogh4, P. Robert1, and N. Cornilleau-Wehrlin1
1Centre d’Etude des Environnements Terrestre et Planétaires, 10/12 avenue de l’Europe, 78140, Vélizy, France
2Laboratoire de Physique et de Chimie de l’Environnement, 3A avenue de la Recherche Scientifique, Orléans, France
3Also at Université Pierre et Marie Curie, Paris, France
4Space and Atmospheric Group, The Blackett laboratory, Imperial College, Prince Consort road, London, UK
Abstract. The spectrum of the magnetic fluctuations measured by the Cluster satellites
in the inner magnetosheath is investigated using the k-filtering technique.
On a case study, it is shown first that the wave vectors calculated from the
Flux Gate Magnetometer (FGM) data fit well with those determined from the
Spatio-Temporal Analysis of Field Fluctuations (STAFF) data for their common
range of frequency, which allows one to confirm that the high pass filter applied
to STAFF data does not alter the spatial characteristics of its spectra. Both
analyses confirm the dominance of the mirror mode for frequencies up to
1.4Hz. Furthermore, by comparing the experimental charateristics of
the identified mirror mode to the prediction of the linear theory, it is
shown that the predicted maximum growth rate is observed in the frequency
range 0-0.15Hz, i.e. the FGM range. All the rest of the mirror
mode, identified for higher frequencies is more likely to be a non linear
extension of the most instable one. This cascade on the spatial scales is, in
turn, observed in the satellite frame as a temporal spread due to Doppler
shift. Further implications on the real nature of the observed spectrum are
discussed.
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