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Ann. Geophys., 23, 997-1011, 2005
www.ann-geophys.net/23/997/2005/
© European Geosciences Union 2005
Correlation between ground-based observations of substorm signatures and magnetotail dynamics
E. Borälv1, H. J. Opgenoorth1,9, K. Kauristie2, M. Lester3, J.-M. Bosqued4, J. P. Dewhurst5, C. J. Owen5, M. Dunlop6,8, J. A. Slavin7, A. Fazakerley5, and C. Perry8
1Swedish Institute of Space Physics, Uppsala, Sweden
2Finnish Meteorological Institute, Space Research, Helsinki, Finland
3University of Leicester, Department of Physics and Astronomy, Leicester, UK
4Centre d’Etude Spatiale des Rayonnements, Toulouse, France
5Mullard Space Science Laboratory, University College London, Surrey, UK
6Space and Atmospheric Physics, Blackett Laboratory, Imperial College, London, UK
7NASA Goddard Space Flight Center, Laboratory for Extraterrestrial Physics, Maryland, USA
8Space Science Department, Rutherford Appleton Laboratory, Oxfordshire, UK
9European Space Agency, ESTEC, Noordwijk, Netherlands
Abstract. We present a substorm event study using the four Cluster spacecraft in
combination with ground-based instruments, in order to perform simultaneous
observations in the ionosphere and magnetotail. We show good correlation
between substorm signatures on the ground and in the magnetotail, even though
data from the northern-ground and southern-tail hemispheres are compared.
During this event ground-based magnetometers show a substorm onset over
Scandinavia in the pre-midnight sector. Within 1.5h the onset and three
intensifications are apparent in the magnetograms. For all the substorm
signatures seen on the ground, corresponding plasma sheet boundary motion is
visible at Cluster, located at a downtail distance of 18.5 RE. As a
result of the substorm onset and intensifications, Cluster moves in and out
between the southern plasma sheet and lobe. Due to the lack of an apparent
solar wind driver and the good correlation between substorm signatures on the
ground, we conclude the substorm itself is the driver for these plasma sheet
dynamics. We show that in the scales of Cluster inter-spacecraft distances
(~0.5 RE) the inferred plasma sheet motion is often directed in
both Ygsm- and Zgsm-directions, and discuss this
finding in the context of previous studies of tail flapping and plasma sheet
thickness variations.
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