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Ann. Geophys., 23, 2877-2887, 2005
www.ann-geophys.net/23/2877/2005/
© European Geosciences Union 2005
Simultaneous Double Star and Cluster FTEs observations on the dawnside flank of the magnetosphere
A. Marchaudon1, C. J. Owen1, J.-M. Bosqued2, R. C. Fear1, A. N. Fazakerley1, M. W. Dunlop3, A. D. Lahiff1, C. Carr4, A. Balogh4, P.-A. Lindqvist5, and H. Rème2
1Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
2Centre d’Etude Spatiale des Rayonnements, CESR/CNRS, B.P. 4346, 31028 Toulouse Cedex, France
3Rutherford-Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
4Space and Atmospheric Physics, Blackett Laboratory, Imperial College, London, SW7 2BZ, UK
5Alfvén Laboratory, Royal Institute of Technology, Stockholm, 10044, Sweden
Abstract. We present Cluster and Double Star-1 (TC-1) observations from a close
magnetic conjunction on 8 May 2004. The five spacecraft were on the
dawnside flank of the magnetosphere, with TC-1 located near the equatorial
plane and Cluster at higher geographic latitudes in the Southern Hemisphere.
TC-1, at its apogee, skimmed the magnetopause for almost 8h (between
08:00-16:00 UT). Flux Transfer Events (FTEs), moving southward/tailward from
the reconnection site, were observed by TC-1 throughout almost all of the
period. Cluster, travelling on a mainly dawn-dusk trajectory, crossed the
magnetopause at around 10:30 UT in the same Magnetic Local Time (MLT) sector
as TC-1 and remained close to the magnetopause boundary layer in the
Southern Hemisphere. The four Cluster spacecraft observed FTEs for a period
of 6.5h between 07:30 and 14:00 UT.
The very clear signatures and the finite transverse sizes of the FTEs
observed by TC-1 and Cluster imply that, during this event, sporadic
reconnection occurred. From the properties of these FTEs, the reconnection
site was located northward of both TC-1 and Cluster on the dawn flank of the
magnetosphere. Reconnection occurred between draped magnetosheath and closed
magnetospheric field lines. Despite variable interplanetary magnetic field
(IMF) conditions and IMF-Bz turnings, the IMF clock angle remained
greater than 70° and the location site appeared to remain relatively
stable in position during the whole period. This result is in agreement with
previous studies which reported that the dayside reconnection remained
active for an IMF clock angle greater than 70°. The simultaneous
observation of FTEs at both Cluster and TC-1, separated by 2h in MLT,
implies that the reconnection site on the magnetopause must have been
extended over several hours in MLT.
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