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Ann. Geophys., 24, 1001-1013, 2006
www.ann-geophys.net/24/1001/2006/
© European Geosciences Union 2006
Alfvén waves in the near-PSBL lobe: Cluster observations
T. Takada1, R. Nakamura1, W. Baumjohann1, K. Seki2, Z. Vörös1, Y. Asano1, M. Volwerk1,3, A. Runov1, T. L. Zhang1, A. Balogh4, G. Paschmann3, R. B. Torbert5, B. Klecker3, H. Rème6, P. Puhl-Quinn5, P. Canu7, and P. M. E. Décréau8
1Space Research Institute, Austrian Academy of Sciences, A-8042 Graz, Austria
2Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
3Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany
4Imperial College, London SW7 2BZ, UK
5University of New Hampshire, Durham, NH 03824, USA
6CESR/CNRS, F-31028 Toulouse Cedex 4, France
7CETP/CNRS and VSQP University, F-78140 Vélizy, France
8LPCE/CNRS and Université d’Orléans, F-45071 Orléans Cedex 2, France
Abstract. Electromagnetic low-frequency waves in the magnetotail lobe close to the
PSBL (Plasma Sheet Boundary Layer) are studied using the Cluster spacecraft.
The lobe waves show Alfvénic properties and transport their wave energy
(Poynting flux) on average toward the Earth along magnetic field lines. Most
of the wave events are rich with oxygen (O+) ion plasma. The rich O+
plasma can serve to enhance the magnetic field fluctuations, resulting in a
greater likelihood of observation, but it does not appear to be necessary
for the generation of the waves. Taking into account the fact that all events
are associated with auroral electrojet enhancements, the source of the lobe
waves might be a substorm-associated instability, i.e. some instability
near the reconnection site, or an ion beam-related instability in the PSBL.
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