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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 10
Ann. Geophys., 23, 3351–3364, 2005
https://doi.org/10.5194/angeo-23-3351-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 3351–3364, 2005
https://doi.org/10.5194/angeo-23-3351-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Nov 2005

30 Nov 2005

Dawn-dusk asymmetries and sub-Alfvénic flow in the high and low latitude magnetosheath

M. Longmore1, S. J. Schwartz2, J. Geach3, B. M. A. Cooling1, I. Dandouras4, E. A. Lucek2, and A. N. Fazakerley5 M. Longmore et al.
  • 1Astronomy Unit, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK
  • 2Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2BW, UK
  • 3Department of Physics, University of Durham, South Road, Durham, DH1 3LE, UK
  • 4CESR-CNRS, 31028 Toulouse Cedex 4, France
  • 5Mullard Space Science Laboratory, Univ. College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, London, UK

Abstract. We present the results of a statistical survey of the magnetosheath using four years of Cluster orbital coverage. Moments of the plasma distribution obtained from the electron and ion instruments together with magnetic field data are used to characterise the flow and density in the magnetosheath. We note two important differences between our survey and the gasdynamic model predictions: a deceleration of the flow at higher latitudes close to the magnetopause, resulting in sub-Alfvénic flow near the cusp, and a dawn-dusk asymmetry with higher velocity magnitudes and lower densities measured on the dusk side of the magnetosheath in the Northern Hemisphere. The latter observation is in agreement with studies carried out by Paularena et al. (2001), Němeček et al. (2000), and Šafránková et al. (2004). In equations of hydrodynamics for a single-component additon to this we observe a reverse of this asymmetry for the Southern Hemisphere. High-latitude sub-Alfvénic flow is thought to be a necessary condition for steady state reconnection pole-ward of the cusp.

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