Fluid description of trains of stationary mirror structures in a magnetized plasma

A simple magnetohydrodynamic model is used to interpret the large-scale features of trains of steady nonlinear magnetic structures, anticorrelated with density, that are commonly observed in anisotropic space plasmas. For this purpose, an equation of state is derived in the quasi-static regime, and stable solutions are obtained, by minimizing the potential energy under the constraint of particle conservation and frozen-in magnetic field. In agreement with satellite observations, these coherent structures take the form of magnetic holes at moderate beta or humps when beta is larger, provided the propagation angle and the anisotropy are sufficiently large. A phenomenon of bistability is also observed, associated with the existence of stable nonlinear structures in a regime where the plasma is stable with respect to the mirror instability. (c) 2006 American Institute of Physics.