Volumes and Issues      Contents of Issue 4

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. Cai^1,2, I. Dandouras¹, H. Rème¹, J. B. Cao², G. C. Zhou², and G. K. Parks^3
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.

Full Article in PDF (1847 KB)