MHD surface type quasi-modes of a current sheet model

Resonantly damped surface type quasi-modes are computed as eigenmodes of the linear dissipative MHD equations for a simple equilibrium model of a current sheet. The current sheet is modeled by a nonuniform plasma layer embedded in a uniform plasma environment. The physical equilibrium variables change in a continuous way in the nonuniform plasma layer. In particular, this is the case with both the strength and the orientation of the equilibrium magnetic field resulting from an electric current in the nonuniform plasma layer. The equilibrium layer can be viewed as a model for a reconnection site in the solar atmosphere or for current sheets in the Earth’s magnetosphere. Two surface type eigenmodes (kink and sausage) are numerically found that can propagate along the nonuniform plasma layer. The phase speeds of these eigenmodes are smaller than the Alfvén speed in the uniform environment. For oblique propagation to the equilibrium magnetic field, the eigenmodes resonantly couple to localized Alfvén waves leading to damped quasi-modes. It is shown that the wave damping is strongly anisotropic and that the dependence of the relative damping rate on the angle of propagation is different for the sausage and the kink type eigenmodes