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Ann. Geophys., 22, 2315-2323, 2004
www.ann-geophys.net/22/2315/2004/
© European Geosciences Union 2004
Alfvén waves in the foreshock propagating upstream in the plasma rest frame: statistics from Cluster observations
Y. Narita1, K.-H. Glassmeier1,2, S. Schäfer1, U. Motschmann3, M. Fränz2, I. Dandouras4, K.-H. Fornaçon1, E. Georgescu5, A. Korth2, H. Rème4, and I. Richter1
1Institut für Geophysik und Meteorologie, TU Braunschweig, Mendelssohnstr. 3, D-38106, Braunschweig, Germany
2Max-Planck-Institut für Aeronomie, Max-Planck-Straße 2, D-37191 Katlenburg-Lindau, Germany
3Institut für Theoretische Physik, TU Braunschweig, Mendelssohnstr. 3, D-38106, Braunschweig, Germany
4CESR/CNRS, 9 Avenue du Colonel Roche, Toulouse Cedex 4, F-31028, France
5Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, D-85748 Garching, Germany
Abstract. We statistically study various properties of low-frequency waves
such as frequencies, wave numbers, phase velocities, and polarization
in the plasma rest frame in the terrestrial foreshock.
Using Cluster observations the wave telescope or k-filtering
is applied to investigate wave numbers and rest frame frequencies.
We find that most of the foreshock waves
propagate upstream along the magnetic field
at phase velocity close to the Alfvén velocity.
We identify that frequencies are around
0.1xΩcp and wave numbers are around
0.1xΩcp/VA, where
Ωcp is the proton cyclotron frequency and VA is the Alfvén velocity.
Our results confirm the conclusions drawn from ISEE observations
and strongly support the existence of Alfvén waves
in the foreshock.
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