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Ann. Geophys., 26, 929-940, 2008
www.ann-geophys.net/26/929/2008/
© European Geosciences Union 2008
Cluster observations on the thin current sheet in the magnetotail
C. L. Cai1,2, I. Dandouras1, H. Rème1, J. B. Cao2, G. C. Zhou2, and G. K. Parks3
1Centre d'Etude Spatiale des Rayonnements, Centre National de la Recherche Scientifique/Université Paul Sabatier, Toulouse 31028, France
2State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Beijing 100080, China
3Space Sciences Laboratory, University of California, Berkeley, CA, 94720, USA
Abstract. A magnetotail event on 15 September 2001 is analyzed, during which the
Cluster spacecraft observed both embedding and bifurcation of the Thin
Current Sheet (TCS). It is indicated that the ion anisotropy and
nongyrotropy are responsible for those new equilibrium features that
represent deviations from the conventional Harris model. Measurements show
that an embedded proton TCS manifests a pressure anisotropy with p||>p⊥, simultaneously associated with a density embedding; while
a bifurcated oxygen ion TCS exhibits a pressure anisotropy mainly with
p||<p⊥ and nongrotropy, except at the edges where p||>p⊥ is the necessary marginal firehose stability condition. The
local flapping motion of the TCS was observed, and some particular features
such as the solitary wave-like behavior and the kink motion in the plane
perpendicular to the Sun-Earth direction were revealed. The present
investigation intimates the complexity of equilibria of the magnetotail current
sheet and declares the crucial role played by the ion kinetics in the
dynamics of TCSs.
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