Anisotropic MHD with gyrokinetic effects

Abstract

With the aim to address the turbulent dynamics of magnetized collisionless plasmas such as the solar wind or the terrestrial magnetosheath, we discuss an extension of anisotropic magnetohydrodynamics that includes a linear description of low‐frequency kinetic effects such as Landau damping and finite Larmor radius (FLR) corrections, in a regime where the small scales are quasi‐transverse (gyrokinetic scaling). The modeling of these additional effects is consistent with the linear kinetic theory and also takes into account the variations of the plasma parameters such as pressures or temperatures, but not the distortion of the magnetic field lines. The model is validated by accurately reproducing the dispersion and collisionless damping of kinetic Alfvén waves, slow waves and large‐scale fast waves, together with the minor instability that develops in an anisotropic plasma with large enough beta. One‐dimensional simulations of the nonlinear dynamics of mirror modes displays in particular magnetic‐hole solutions in linearly stable plasmas, in agreement with satellite observations in planetary magnetosheaths. Further developments should include the modeling of particle trapping needed to arrest linear Landau damping, and also the effect of local variations of the magnetic field intensity on the FLR corrections.