Articles | Volume 30, issue 3
Ann. Geophys., 30, 583–595, 2012

Special issue: Cluster 10th anniversary workshop

Ann. Geophys., 30, 583–595, 2012

  26 Mar 2012

26 Mar 2012

Cluster and TC-1 observation of magnetic holes in the plasma sheet

W. J. Sun1,2, Q. Q. Shi1, S. Y. Fu3, Z. Y. Pu3, M. W. Dunlop4, A. P. Walsh5, Q. G. Zong3, T. Xiao1, C. L. Tang1, H. Reme6,7, C. Carr8, E. Lucek8, and A. Fazakerley5 W. J. Sun et al.
  • 1Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University at Weihai, Weihai, China
  • 2State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, China
  • 3Institute of Space Physics and Applied Technology, Peking University, Beijing, China
  • 4Rutherford Appleton Laboratory, Didcot OX11 0QX, UK
  • 5Mullard Space Science Laboratory, University College London, Holmbury St. Mary Dorking, Surrey RH5 6NT, UK
  • 6Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
  • 7CNRS; IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse cedex 4, France
  • 8Space and Atmospheric Physics, the Blackett Laboratory, Imperial College, London, UK

Abstract. Magnetic holes with relatively small scale sizes, detected by Cluster and TC-1 in the magnetotail plasma sheet, are studied in this paper. It is found that these magnetic holes are spatial structures and they are not magnetic depressions generated by the flapping movement of the magnetotail current sheet. Most of the magnetic holes (93%) were observed during intervals with Bz larger than Bx, i.e. they are more likely to occur in a dipolarized magnetic field topology. Our results also suggest that the occurrence of these magnetic holes might have a close relationship with the dipolarization process. The magnetic holes typically have a scale size comparable to the local proton Larmor radius and are accompanied by an electron energy flux enhancement at a 90° pitch angle, which is quite different from the previously observed isotropic electron distributions inside magnetic holes in the plasma sheet. It is also shown that most of the magnetic holes occur in marginally mirror-stable environments. Whether the plasma sheet magnetic holes are generated by the mirror instability related to ions or not, however, is unknown. Comparison of ratios, scale sizes and propagation direction of magnetic holes detected by Cluster and TC-1, suggests that magnetic holes observed in the vicinity of the TC-1 orbit (~7–12 RE) are likely to be further developed than those observed by Cluster (~7–18 RE).