Analysis of mirror modes convected from the bow shock to the magnetopause

Spacecraft observations confirm the existence of mirror fluctuations in the magnetosheath. The mirror instability occurs in an anisotropic magnetized plasma when the difference between perpendicular and parallel (with respect to the magnetic field) plasma pressure exceeds a threshold depending on th e perpendicular plasma beta. The anisotropy of the plasma pressure increase s from the shock to the magnetopause as a result of magnetic field line str etching. This gives rise to plasma fluctuations which in turn lead to a rel axation between parallel and perpendicular temperatures. Mirror perturbatio ns do not propagate and are convected with plasma flow along the streamline s. Using an anisotropic steady-state MHD flow model, we calculate the growt h of mirror fluctuations from the bow shock to the magnetopause along the s ubsolar streamline. For the anisotropic MHD model, we use the empirical clo sure equation suitable for the AMPTE/IRM observations. The amplitudes of mi rror fluctuations, which are obtained as a function of distance from the ma gnetopause, are directly compared with AMPTE/IRM observations on October 24 , 1985. With regard to both the amplification of the magnetic field and the plasma density oscillations, as well as the location of maximum amplitudes , model calculations are in good agreement with values obtained from the AM PTE/IRM data. (C) 2001 Elsevier Science Ltd. All rights reserved.