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Ann. Geophys., 24, 247-262, 2006
www.ann-geophys.net/24/247/2006/
© European Geosciences Union 2006
Local structure of the magnetotail current sheet: 2001 Cluster observations
A. Runov1, V. A. Sergeev2, R. Nakamura1, W. Baumjohann1, S. Apatenkov2, Y. Asano1, T. Takada1, M. Volwerk1,3, Z. Vörös1, T. L. Zhang1, J.-A. Sauvaud4, H. Rème4, and A. Balogh5
1Space Research Institute, Austrian Academy of Sciences, A-8042 Graz, Austria
2St. Petersburg University, St. Petersburg, Russia
3MPE, Garching, Germany
4CESR/CNRS, Toulouse, France
5IC, London, UK
Abstract. Thirty rapid crossings of the magnetotail current sheet
by the Cluster spacecraft during July-October
2001 at a geocentric
distance of 19 RE are examined in detail to address the structure of the current
sheet. We use four-point magnetic field measurements to estimate electric current
density; the current sheet spatial scale is estimated by integration of
the translation velocity calculated from the magnetic field temporal and
spatial derivatives. The local normal-related coordinate system for each
case is defined by the combining Minimum Variance Analysis (MVA) and the curlometer
technique. Numerical parameters characterizing the plasma sheet
conditions for these crossings are provided to facilitate future
comparisons with theoretical models. Three types of current sheet
distributions are distinguished: center-peaked (type I),
bifurcated (type II) and asymmetric (type III) sheets.
Comparison to plasma parameter distributions show that practically all
cases display non-Harris-type behavior, i.e. interior current peaks
are embedded into a thicker plasma sheet. The asymmetric sheets with
an off-equatorial current density peak most likely have a transient
nature.
The ion contribution to the electric current rarely agrees with the
current computed using the curlometer technique,
indicating that either the electron contribution to the
current is strong and variable, or the current density is spatially or temporally structured.
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