|
|
 |
|
|
Ann. Geophys., 23, 973-982, 2005
www.ann-geophys.net/23/973/2005/
© European Geosciences Union 2005
Optimal reconstruction of magnetopause structures from Cluster data
H. Hasegawa1,2, B. U. Ö. Sonnerup1, B. Klecker2, G. Paschmann2, M. W. Dunlop3, and H. Rème4
1Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
2Max-Planck-Institut für extraterrestrische Physik, Garching, Germany
3Space Sciences Division, Rutherford Appleton Laboratory, Oxfordshire, UK
4Centre d’Etude Spatiale des Rayonnements, Toulouse, France
Abstract. The Grad-Shafranov (GS) reconstruction technique, a single-spacecraft based
data analysis method for recovering approximately two-dimensional (2-D)
magnetohydrostatic plasma/field structures in space, is improved to become a
multi-spacecraft technique that produces a single field map by ingesting data
from all four Cluster spacecraft into the calculation. The plasma pressure,
required for the technique, is measured in high time resolution by only two
of the spacecraft, C1 and C3, but, with the help of spacecraft potential
measurements available from all four spacecraft, the pressure can be
estimated at the other spacecraft as well via a relationship, established
from C1 and C3 data, between the pressure and the electron density deduced
from the potentials. Consequently, four independent field maps, one for each
spacecraft, can be reconstructed and then merged into a single map. The
resulting map appears more accurate than the individual single-spacecraft
based ones, in the sense that agreement between magnetic field variations
predicted from the map to occur at each of the four spacecraft and those
actually measured is significantly better. Such a composite map does not
satisfy the GS equation any more, but is optimal under the constraints that
the structures are 2-D and time-independent. Based on the reconstruction
results, we show that, even on a scale of a few thousand km, the magnetopause
surface is usually not planar, but has significant curvature, often with
intriguing meso-scale structures embedded in the current layer, and that the
thickness of both the current layer and the boundary layer attached to its
earthward side can occasionally be larger than 3000km.
Full Article in PDF (2823 KB) |
|
|
