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Ann. Geophys., 22, 2597-2606, 2004
www.ann-geophys.net/22/2597/2004/
© European Geosciences Union 2004
Characteristics of magnetospherically reflected chorus waves observed by CLUSTER
M. Parrot1, O. Santolík2, D. A. Gurnett3, J. S. Pickett3, and N. Cornilleau-Wehrlin4
1LPCE/CNRS, 3A Avenue de la Recherche, Orléans, 45071, France
2Charles University, Faculty of Mathematics and Physics, V Holesovickach 2, Praha 8, 18000, Czech Republic
3Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242-1479, USA
4CETP/UVSQ, 10/12 Avenue de l’Europe, Velizy, 78140, France
Abstract. Chorus emissions are often observed by the STAFF spectrum
analyser on board the 4 satellites of CLUSTER. This instrument provides
the cross spectral matrix of three magnetic and two electric field
components. Dedicated software processes this spectral matrix in order to
determine the propagation characteristic of these chorus waves. Measurements
of the parallel component of the Poynting vector around the magnetic equator
indicate that the chorus waves propagate away from this region which is
considered as the source area of these emissions. This is valid for the most
intense waves observed on the magnetic and electric power spectrograms. But
it has also been observed that lower intensity waves propagate toward the
equator at the same frequency. Using the wave normal directions of these
waves, a ray tracing study has shown that the waves have suffered a Lower
Hybrid Resonance (LHR) reflection at low altitudes and now return to the
equator at a different location with a lower intensity. The paper presents
other similar events when WBD data are simultaneously recorded. The WBD
experiment provides a much better time resolution and allows one to check the
structure of the returning waves. It is observed that these waves have still
a high degree of polarization, even if they started to lose the coherent
structure of the chorus elements. They reach the equator with a small wave
normal angle which is more efficient for a further amplification. It is
explained that these emissions could be a source of hiss.
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