Hall MHD Ballooning Instability in the Magnetotail: A Possible Mechanism for Substorm Onset

Details Hall MHD Ballooning Instability in the Magnetotail: A Possible Mechanism for Substorm Onset Hall MHD Ballooning Instability in the Magnetotail: A Possible Mechanism for Substorm Onset

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm71a0570z&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SM71A-0570

Physics

2744 Magnetotail, 2752 Mhd Waves And Instabilities, 2788 Storms And Substorms

Scientific paper

The ballooning instability of the magnetotail is considered within the framework of the Hall MHD model. In particular, the extent to which Hall MHD effects modify the ideal MHD ballooning instability is explored extensively. It is shown that Hall MHD effects primarily enter the stability analysis through changes in the plasma compressibility. In addition to modifying the growth rate of the compressible ideal MHD mode, Hall effects also introduce a new instability, called the entropy interchange instability which is a variant of the well-known ion temperature gradient instability. The theory is applied to two types of magnetotail configurations---analytic equilibria [Voigt 1986], and more realistic magnetotail configurations containing thin current sheets obtained from Hall MHD simulations of substorm dynamics [Ma and Bhattacharjee 1998]. It is shown that Hall effects introduce an oscillatory component to the purely growing MHD instability, consistent with the westward traveling surge seen in current disruption events at near-Earth distances. Even in the presence of line-tying constraints imposed by the ionosphere, the ballooning instability of collisionless thin current sheets continues to be robust, and a viable candidate for substorm onset.

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