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Ann. Geophys., 20, 405-426, 2002
www.ann-geophys.net/20/405/2002/
© European Geosciences Union 2002
Coordinated ground-based and Cluster observations of large amplitude global magnetospheric oscillations during a fast solar wind speed interval
I. R. Mann1, I. Voronkov2, M. Dunlop3, E. Donovan4, T. K. Yeoman5, D. K. Milling1, J. Wild5, K. Kauristie6, O. Amm6, S. D. Bale7, A. Balogh3, A. Viljanen6, and H. J. Opgenoorth8
1Department of Physics, University of York, York, UK
2Department of Physics, University of Alberta, Edmonton, Alberta, Canada
3Imperial College, London, UK
4Department of Physics and Astronomy, University of Calgary, Alberta, Canada
5Department of Physics and Astronomy, University of Leicester, Leicester, UK
6Finnish Meteorological Institute, Geophysical Research Division, P.O. Box 503, FIN-00101, Helsinki, Finland
7Space Sciences Laboratory, University of California, Berkeley, USA
8Swedish Institute of Space Physics, Uppsala Division, Sweden
Correspondence to: I. R. Mann (ian@aurora.york.ac.uk)
Abstract. We present magnetospheric
observations of very large amplitude global scale ULF waves, from 9 and 10
December 2000 when the upstream solar wind speed exceeded 600 km/s. We
characterise these ULF waves using ground-based magnetometer, radar and optical
instrumentation on both the dawn and dusk flanks; we find evidence to support
the hypothesis that discrete frequency field line resonances (FLRs) were being
driven by magnetospheric waveguide modes. During the early part of this
interval, Cluster was on an outbound pass from the northern dusk side
magnetospheric lobe into the magnetosheath, local-time conjugate to the
Canadian sector. In situ magnetic fluctuations, observed by Cluster FGM, show
evidence of quasi-periodic motion of the magnetosheath boundary layer with the
same period as the ULF waves seen on the ground. Our observations represent the
first simultaneous magnetometer, radar and optical observations of the
characteristics of FLRs, and confirm the potential importance of ULF waves for
magnetosphere-ionosphere coupling, particularly via the generation and
modulation of electron precipitation into the ionosphere. The in situ Cluster
measurements support the hypothesis that, during intervals of fast solar wind
speed, the Kelvin-Helmholtz instability (KHI) can excite magnetospheric
waveguide modes which bathe the flank magnetosphere with discrete frequency ULF
wave power and drive large amplitude FLRs.
Paper submitted to the special issue devoted to
"Cluster: First scientific results", Ann. Geophysicae, 19, 10/11/12,
2001.
Key words. Magnetospheric physics
(magnetopause, cusp and boundary layers; MHD waves and instabilities; solar
wind-magnetosphere interactions)
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