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Ann. Geophys., 23, 2199-2215, 2005
www.ann-geophys.net/23/2199/2005/
© European Geosciences Union 2005
Cluster observation of continuous reconnection at dayside magnetopause in the vicinity of cusp
Y. Zheng1, G. Le2, J. A. Slavin2, M. L. Goldstein2, C. Cattell3, A. Balogh4, E. A. Lucek4, H. Rème5, J. P. Eastwood1, M. Wilber6, G. Parks6, A. Retinò7, and A. Fazakerley8
1National Research Council, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
2Lab. for Solar and Space Phys., Earth-Sun Explor. Div., NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
3University of Minnesota, School of Physics and Astronomy, Tate Lab, Minneapolis, MN 55455, USA
4Imperial College, Department of Space and Atmospheric Physics, London, UK
5CESR, BP4346, 31028 Toulouse Cedex 4, Toulouse, France
6Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
7Swedish Institute of Space Physics, Uppsala Division, Uppsala, Sweden
8Dept. of Phys., Mullard Space Sci. Lab., Univ. College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
Abstract. In this paper, we present a case study of continuous reconnection at the
dayside magnetopause observed by the Cluster spacecraft. On 1 April 2003, the
four Cluster spacecraft experienced multiple encounters with the Earth's dayside
magnetopause under a fairly stable southwestward interplanetary magnetic
field (IMF). Accelerated plasma flows, whose magnitude and direction are
consistent with the predictions of the reconnection theory (the Walén
relation), were observed at and around the magnetopause current layer for a
prolonged interval of ~3 h at two types of magnetopause crossings,
one with small magnetic shears and the other one with large magnetic shears.
Reversals in the Y component of ion bulk flow between the magnetosheath and
magnetopause current layer and acceleration of magnetosheath electrons were
also observed. Kinetic signatures using electron and ion velocity
distributions corroborate the interpretation of continuous magnetic
reconnection. This event provides strong in-situ evidence that magnetic
reconnection at the dayside magnetopause can be continuous for many hours.
However, the reconnection process appeared to be very dynamic rather than
steady, despite the steady nature of the IMF. Detailed analysis using
multi-spacecraft magnetic field and plasma measurements shows that the
dynamics and structure of the magnetopause current layer/boundary can be very
complex. For example, highly variable magnetic and electric fields were
observed in the magnetopause current layer. Minimum variance analysis shows
that the magnetopause normal deviates from the model normal. Surface waves
resulting from the reconnection process may be involved in the oscillation of
the magnetopause.
Keywords. Magnetospheric physics (Magnetopause, cusp
and boundary layers; Solar wind-magnetosphere interactions)
– Space plasma physics (magnetic reconnection)
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