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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 23, issue 2
Ann. Geophys., 23, 609-624, 2005
https://doi.org/10.5194/angeo-23-609-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 23, 609-624, 2005
https://doi.org/10.5194/angeo-23-609-2005
© Author(s) 2005. This work is distributed under
the Creative Commons Attribution 3.0 License.

  28 Feb 2005

28 Feb 2005

Cluster observations of sudden impulses in the magnetotail caused by interplanetary shocks and pressure increases

K. E. J. Huttunen1, J. Slavin2, M. Collier2, H. E. J. Koskinen1,3, A. Szabo2, E. Tanskanen2, A. Balogh4, E. Lucek4, and H. Rème5 K. E. J. Huttunen et al.
  • 1Department of Physical Sciences, P.O. Box 64, FIN-00014 University of Helsinki, Finland
  • 2Laboratory for Extraterrestial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland
  • 3Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
  • 4Blackett Laboratory, Imperial College, London, England
  • 5Centre d’Etude Spatiale des Rayonnements, Toulouse, France

Abstract. Sudden impulses (SI) in the tail lobe magnetic field associated with solar wind pressure enhancements are investigated using measurements from Cluster. The magnetic field components during the SIs change in a manner consistent with the assumption that an antisunward moving lateral pressure enhancement compresses the magnetotail axisymmetrically. We found that the maximum variance SI unit vectors were nearly aligned with the associated interplanetary shock normals. For two of the tail lobe SI events during which Cluster was located close to the tail boundary, Cluster observed the inward moving magnetopause. During both events, the spacecraft location changed from the lobe to the magnetospheric boundary layer. During the event on 6 November 2001 the magnetopause was compressed past Cluster. We applied the 2-D Cartesian model developed by collier98 in which a vacuum uniform tail lobe magnetic field is compressed by a step-like pressure increase. The model underestimates the compression of the magnetic field, but it fits the magnetic field maximum variance component well. For events for which we could determine the shock normal orientation, the differences between the observed and calculated shock propagation times from the location of WIND/Geotail to the location of Cluster were small. The propagation speeds of the SIs between the Cluster spacecraft were comparable to the solar wind speed. Our results suggest that the observed tail lobe SIs are due to lateral increases in solar wind dynamic pressure outside the magnetotail boundary.

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