Consequences of Nongyrotropy in Magnetohydrodynamics
It is assumed in the MHD set of equations that a plasma is both isotropic and gyrotropic at any instant of time. However, this cannot be always justified for applications in space plasmas which are essentially collisionless. By introducing two relaxation time scales, one for isotropization and another for gyrotropization, we propose a model which describes evolution of the field and the plasma variables, including all the pressure tensor elements. We evaluate the linear wave dispersion relation of the system, and then apply the model to various space plasma phenomena.

Normalized damping rate of the fast and slow mode waves plotted versus the isotropization time scale.

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