Finite ky ballooning instability in the near-Earth magnetotail

P. Zhu, A. Bhattacharjee, Z. W. Ma

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Two-dimensional initial value MHD simulations of the linear ideal MHD ballooning instability in the near-Earth magnetotail are presented. The configuration of the magnetotail is modeled by the analytic two-dimensional static equilibrium developed by Voigt. For an intermediate range of plasma β values (∼1-100) at the equatorial plane, the Voigt configuration of the near-Earth magnetotail is shown to be unstable to ballooning modes with finite ky (A similar intermediate range of plasma β was also obtained in the stability analyses of ballooning modes in the infinite k y limit.) Such a β dependence of the instability arises because of the stabilizing effect of plasma compression involved in the ballooning displacement of flux tubes in the high-β regime of the magnetotail. The growth rate of the finite ky ballooning instability is found to increase with-the wave number ky, approaching a saturated value in the very large ky limit. The thinning of the current sheet is found to enhance the regime of unstable β as well as the growth rate of the linear ballooning instability of the near-Earth magnetotail, suggesting a possible scenario for the substorm trigger.

Original languageEnglish (US)
Article numberA11211
JournalJournal of Geophysical Research: Space Physics
Issue numberA11
StatePublished - Nov 2004
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Space and Planetary Science


  • Ballooning instability
  • MHD simulation
  • Magnetotail
  • Substorm onset
  • Trigger


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