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Ann. Geophys., 19, 1697-1709, 2001
www.ann-geophys.net/19/1697/2001/
© European Geosciences Union 2001
Identification of natural plasma emissions observed close to the plasmapause by the Cluster-Whisper relaxation sounder
P. Canu1, P. M. E. Décréau2, J. G. Trotignon2, J. L. Rauch3, H. C. Seran3, P. Fergeau3, M. Lévêque3, Ph. Martin3, F. X. Sené3, E. Le Guirriec3, H. Alleyne4, and K. Yearby4
1CETP/CNRS/UVSQ, 10–12 Avenue de l’Europe,78140 Vélizy, France
2LPCE/CNRS and Université d’Orléans, 3A Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
3LPCE/CNRS, 3A Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France
4University of Sheffield, Sheffield, S1 4DU, UK
Abstract. We use the data collected
by the Whisper instrument onboard the Cluster spacecraft for a first test of
its capabilities in the identification of the natural plasma waves observed in
the Earth’s magnetosphere. The main signatures observed at the plasma
frequency, upper hybrid frequency, and electron Bernstein modes were often
difficult to be reliably recognized on previous missions. We use here the
characteristic frequencies provided by the resonances triggered by the
relaxation sounder of Whisper to identify with good confidence the various
signatures detected in the complex wave spectra collected close to the
plasmapause. Coupled with the good sensitivity, frequency and time resolution
of Whisper, the resonances detected by the sounder allow one to precisely spot
these natural emissions. This first analysis seems to confirm the
interpretation of Geos observations: the natural emissions observed in
Bernstein modes above the plasma frequency, now widely observed onboard
Cluster, are not modeled by a single Maxwellian electrons distribution
function. Therefore, multi-temperature electron distribution functions should
be considered.
Key words. Space plasma physics
(active perturbation experiments; waves and instabilities; instrument and
techniques)
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