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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 12
Ann. Geophys., 22, 4143–4151, 2004
https://doi.org/10.5194/angeo-22-4143-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 4143–4151, 2004
https://doi.org/10.5194/angeo-22-4143-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  22 Dec 2004

22 Dec 2004

Radial dependence of foreshock cavities: a case study

D. G. Sibeck1, K. Kudela2, T. Mukai3, Z. Nemecek4, and J. Safrankova4 D. G. Sibeck et al.
  • 1NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA
  • 2Institute of Experimental Physics Slovak Academy of Sciences, Kosice, Slovakia
  • 3Institute of Space and Astronautical Sciences, Kanagawa, Japan
  • 4Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic

Abstract. We present a case study of Geotail, Interball-1, IMP-8, and Wind observations of density and magnetic field strength cavities excavated by the enhanced pressures associated with bursts of energetic ions in the foreshock. Consistent with theoretical predictions, the pressure of the energetic ions diminishes rapidly with upstream distance due to a decrease in the flux of energetic ions and a transition from near-isotropic to streaming pitch angle distributions. Consequently, the cavities can only be observed immediately upstream from the bow shock. A comparison of conditions upstream from the pre- and post-noon bow shock demonstrates that foreshock cavities introduce perturbations into the oncoming solar wind flow with dimensions smaller than those of the magnetosphere. Dayside geosynchronous magnetic field strength variations observed by GOES-8 do not track the density variations seen by any of the spacecraft upstream from the bow shock in a one-to-one manner, indicating that none of these spacecraft observed the precise sequence of density variations that actually struck the subsolar magnetopause.

Key words. Interplanetary physics (energetic particles; planetary bow shocks) – Magnetospheric physics (solar wind-magnetosphere interactions)

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