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Ann. Geophys., 20, 1699-1710, 2002
www.ann-geophys.net/20/1699/2002/
© European Geosciences Union 2002
Cluster magnetic field observations at a quasi-parallel bow shock
E. A. Lucek1, T. S. Horbury1, M. W. Dunlop1, P. J. Cargill1, S. J. Schwartz2, A. Balogh1, P. Brown1, C. Carr1, K.-H. Fornacon3, and E. Georgescu4,5
1Space and Atmospheric Physics, The Blackett Laboratory, Imperial College, London, UK
2Astronomy Unit, Queen Mary, University of London, London, UK
3Institut für Geophysik und Meteorlogie, Technische Universität Braunschweig, Germany
4Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany
5Institut of Space Sciences, Bucharest, Romania
Correspondence to: E. A. Lucek (e.lucek@ic.ac.uk)
Abstract. We present four-point
Cluster magnetic field data from a quasi-parallel shock crossing which allows
us to probe the three-dimensional structure of this type of shock for the first
time. We find that steepened ULF waves typically have a scale larger than the
spacecraft separation ( ~ 400–1000 km), while SLAMS-like magnetic field
enhancements have different signatures in | B | at the four spacecraft,
suggesting that they have a smaller scale size. In the latter case, however,
the angular variations of B are similar, consistent with the space-craft
making different trajectories through the same structure. The field
enhancements have different orientations relative to a model bow shock normal,
which might arise from different degrees of deceleration and deflection of the
surrounding solar wind plasma. The observed rotation of the magnetic field
rising from a direction approximately parallel to the model bow shock normal to
a direction more perpendicular to the model normal across the field enhancement
is consistent with previously published results. Successive magnetic field
enhancements or ULF waves, and the leading and trailing edges of the same
structure, are found to have different orientations.
Key words. Interplanetary physics
(planetary bow shocks)
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