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Ann. Geophys., 19, 1579-1587, 2001
www.ann-geophys.net/19/1579/2001/
© European Geosciences Union 2001
Preliminary two-point observations of the mid-altitude cusp by Cluster PEACE and FGM
I. Krauklis1, A. N. Fazakerley1, C. J. Owen1, P. J. Carter1, M. W. Dunlop2, A. J. Coates1, S. Szita1, M. G. G. T. Taylor1, P. Travnicek1, G. Watson1, and R. J. Wilson1
1Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, UK
2Blackett Laboratory, Imperial College of Science Technology and Medicine, London, UK
Abstract. On 1 October 2000,
Cluster spacecraft Samba (Cluster 3) and Tango (Cluster 4) made an outbound
crossing of the northern mid-altitude (4.7 RE) cusp region,
moving roughly parallel to the noon meridian. We present preliminary
observations from this interval made by the PEACE and FGM instruments. The
interplanetary magnetic field at the magnetopause is estimated to have turned
south at the time of our observations, based on ACE data as well as a rough
estimate of the time taken for the solar wind to travel between ACE and the
magnetopause. Cluster 3 encountered the low-latitude boundary layer (LLBL)
between 12:20:30 to 12:26:00 UT, and the cusp region between 12:26:00 and
12:32:30 UT. Cluster 4 encountered the LLBL between 12:22:00 to 12:29:00 UT,
and the cusp region between 12:29:00 and 12:38:00 UT. During the interval
between the two spacecraft passages through these regions, the open/closed
field line boundary was observed to move equatorward by 0.33° invariant
latitude, while the latitudinal extent of the cusp region increased by 0.5°.
Both of these observations are consistent with the ongoing reconnection at the
sub-solar magnetopause. The magnetic field data indicate that Cluster
encountered four field-aligned longitudinally extended current sheets. The most
equatorward of these is consistent with the location of a Region 1 current
sheet. Two current sheets were observed in the vicinity of the cusp region,
though neither of these were thin current sheets. The fourth current sheet was
observed in the mantle region and was largely unaffected by the latitudinal
expansion of the cusp region.
Key words. Magnetospheric physics
(current systems; energetic particles, precipitating; magnetopause, cusp and
boundary layers)
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