Effects of finite Larmor radius and equilibrium shear flow on ideal MHD Stability

Details Effects of finite Larmor radius and equilibrium shear flow on ideal MHD Stability Effects of finite Larmor radius and equilibrium shear flow on ideal MHD Stability

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm31a0753w&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SM31A-0753

Physics

2736 Magnetosphere/Ionosphere Interactions, 2744 Magnetotail, 2788 Storms And Substorms

Scientific paper

During magnetic substorms in the Earth's magnetosphere, auroral brightening due to electron precipitation is observed to rapidly appear on field lines that intersect the the night-side equatorial plane at 6-12 Earth radii. This suggests that pressure gradient driven ballooning magnetohydrodyanmic (MHD) instabilities, with their kinetic modifications, may be responsible for the perturbations in the associated magnetic flux tubes. Many investigations have been based on conventional MHD energy functional which requires small ion gyoradius and frequencies very low compare with the ion cyclotron frequency for their validity. In the auroral field line region these approximations are breaking down for the instabilities space-time scales required to explain the auroral brightening phenomenon. An investigation of plasma instabilities valid for arbitrary ion Larmor radius and including sheared flows has been initiated for this region. We use a simple pinch geometry to describe the large crosstail plasma current and high pressure gradients in the plasma in this region. The single particle constants of the motion are used to construct the equilbrium. The plasma beta, the collisionless ion skin depth, and the flow shear are key parameters of the stability problem. The integral eigenvalue problem is solved for the full three components of the electromagnetic pertubations. The polarization of the most unstable modes is determined. The stability and dynamical differences between the kinetic and the standard single fluid MHD are then presented in relation to the substorm problem. This work is supported by the NSF-ATM and the US Department of Energy.

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