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Volume 22, issue 4
Ann. Geophys., 22, 1347–1365, 2004
https://doi.org/10.5194/angeo-22-1347-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 1347–1365, 2004
https://doi.org/10.5194/angeo-22-1347-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  02 Apr 2004

02 Apr 2004

Four-spacecraft determination of magnetopause orientation, motion and thickness: comparison with results from single-spacecraft methods

S. E. Haaland5,1, B. U. Ö. Sonnerup2, M. W. Dunlop3, A. Balogh4, E. Georgescu5, H. Hasegawa2, B. Klecker5, G. Paschmann5,1, P. Puhl-Quinn5, H. Rème6, H. Vaith5, and A. Vaivads7 S. E. Haaland et al.
  • 1International Space Science Institute (ISSI), Bern, Switzerland
  • 2Dartmouth College, Hanover, NH, USA
  • 3Rutherford-Appleton Labs, Oxford, UK
  • 4Imperial College, London, UK
  • 5Max-Planck Institute für extraterrestrische Physik (MPE), Garching, Germany
  • 6Centre d’Étude Spatiale des Rayonnements (CESR), Toulouse, France
  • 7Swedish Institute of Space Physics, Uppsala, Sweden

Abstract. In this paper, we use Cluster data from one magnetopause event on 5 July 2001 to compare predictions from various methods for determination of the velocity, orientation, and thickness of the magnetopause current layer. We employ established as well as new multi-spacecraft techniques, in which time differences between the crossings by the four spacecraft, along with the duration of each crossing, are used to calculate magnetopause speed, normal vector, and width. The timing is based on data from either the Cluster Magnetic Field Experiment (FGM) or the Electric Field Experiment (EFW) instruments. The multi-spacecraft results are compared with those derived from various single-spacecraft techniques, including minimum-variance analysis of the magnetic field and deHoffmann-Teller, as well as Minimum-Faraday-Residue analysis of plasma velocities and magnetic fields measured during the crossings. In order to improve the overall consistency between multi- and single-spacecraft results, we have also explored the use of hybrid techniques, in which timing information from the four spacecraft is combined with certain limited results from single-spacecraft methods, the remaining results being left for consistency checks. The results show good agreement between magnetopause orientations derived from appropriately chosen single-spacecraft techniques and those obtained from multi-spacecraft timing. The agreement between magnetopause speeds derived from single- and multi-spacecraft methods is quantitatively somewhat less good but it is evident that the speed can change substantially from one crossing to the next within an event. The magnetopause thickness varied substantially from one crossing to the next, within an event. It ranged from 5 to 10 ion gyroradii. The density profile was sharper than the magnetic profile: most of the density change occured in the earthward half of the magnetopause.

Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; instruments and techniques) – Space plasma physics (discontinuities)

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