Published online by Cambridge University Press: 13 March 2009
Weakly nonlinear surface waves rippling an MHD tangential discontinuity (TD) of finite thickness are studied. The waves are two-dimensional and evanescent in the direction normal to the inhomogeneous layer. A novel approach is utilized to treat weakly nonlinear evanescent wave fields in physical space. The evolution equation obtained, which governs the interface displacement as a function of time and position, extends previous results of Ruderman and Goossens, valid for propagation along a unidirectional magnetic field in a stationary incompressible plasma, to a TD of general field geometry in a compressible plasma in the presence of stable velocity shear. Certain conservation properties of the evolution equation are presented, including the Hamiltonian formulation. Exploratory numerical results are reported. The model is of potential use in the analysis of observed quasi-stationary perturbations at the earth's magnetopause.