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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 11
Ann. Geophys., 24, 3131-3137, 2006
https://doi.org/10.5194/angeo-24-3131-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 3131-3137, 2006
https://doi.org/10.5194/angeo-24-3131-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  22 Nov 2006

22 Nov 2006

The cusp: a window for particle exchange between the radiation belt and the solar wind

X.-Z. Zhou1,2, T. A. Fritz3, Q.-G. Zong2,4, Z. Y. Pu1, Y.-Q. Hao1, and J.-B. Cao2 X.-Z. Zhou et al.
  • 1Institute of Space Physics and Applied Technology, Peking University, Beijing 100871, China
  • 2Key Laboratory for Space Weather, Chinese Academy of Sciences, Beijing, China
  • 3Center for Space Physics, Boston University, Boston, MA 02215, USA
  • 4Center for Atmospheric Research, University of Massachusetts, Lowell, MA 01854, USA

Abstract. The study focuses on a single particle dynamics in the cusp region. The topology of the cusp region in terms of magnetic field iso-B contours has been studied using the Tsyganenko 96 model (T96) as an example, to show the importance of an off-equatorial minimum on particle trapping. We carry out test particle simulations to demonstrate the bounce and drift motion. The "cusp trapping limit" concept is introduced to reflect the particle motion in the high latitude magnetospheric region. The spatial distribution of the "cusp trapping limit" shows that only those particles with near 90° pitch-angles can be trapped and drift around the cusp. Those with smaller pitch angles may be partly trapped in the iso-B contours, however, they will eventually escape along one of the magnetic field lines. There exist both open field lines and closed ones within the same drift orbit, indicating two possible destinations of these particles: those particles being lost along open field lines will be connected to the surface of the magnetopause and the solar wind, while those along closed ones will enter the equatorial radiation belt. Thus, it is believed that the cusp region can provide a window for particle exchange between these two regions. Some of the factors, such as dipole tilt angle, magnetospheric convection, IMF and the Birkeland current system, may influence the cusp's trapping capability and therefore affect the particle exchanging mechanism. Their roles are examined by both the analysis of cusp magnetic topology and test particle simulations.

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