Anisotropic MHD model and some solutions

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MHD waves and instabilities in a collisionless anisotropic-pressure plasma are analyzed in an anisotropic MHD model based on the 16-moment approximation, and the results are found to agree well with those obtained in the low-frequency limit of the kinetic model. It is shown that accounting for heat fluxes leads to an asymmetry in the phase velocities of the wave modes with respect to the heat flux direction and also to a strong interaction between the modes, especially between the backward ones (those that propagate in a direction opposite to that of the heat flux). A correct description of the mirror instability is given. The resonant interaction of three backward modes—fast acoustic, fast magnetosonic, and slow acoustic—under the conditions for the onset of the classical firehose instability triggers a new type of instability the growth rate of which is faster than the maximum growth rate of the conventional firehose instability. The results prove that, in contrast to the familiar Chew-Goldberger-Low approximate model, the anisotropic MHD approach provides a correct description of the large-scale dynamics of collisionless anisotropic plasmas (such as solar corona, solar wind, and ionospheric and magnetospheric plasmas).

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Theoretical or Mathematical/ method of moments plasma instability plasma kinetic theory plasma magnetohydrodynamic waves plasma magnetohydrodynamics plasma oscillations/ MHD waves anisotropic MHD model collisionless anisotropic-pressure plasma kinetic model wave mode phase velocity heat flux direction mirror instability fast acoustic backward mode fast magnetosonic backward mode slow acoustic backward mode firehose instability large-scale dynamics oscillatory MHD instability 16-moment approximation Chew-Goldberger-Low approximate model/ A5235B Plasma magnetohydrodynamic waves, Alfven and hydromagnetic waves A5230 Plasma flow magnetohydrodynamics A5235P Plasma instabilities A5235F Plasma electrostatic waves and oscillations A5225D Plasma kinetic equations A0260 Numerical approximation and analysis