Resonant surface waves and instabilities in finite beta plasmas

摘要

Magnetohydrodynamic surface waves are studied at an interface of finite thickness separating two homogeneous arbitrary finite beta plasmas which are in parallel motion with respect to each other and are permeated by parallel magnetic fields. It is assumed that the density decreases and the magnetic field strength increases across the interface. The model is representative of the mantle-like boundary layer separating the fast flowing magnetosheath from the tail region of the magnetosphere. All existing wave modes are classified, their main properties are investigated, and analytical expressions for critical velocities are obtained. The resonant flow instability (RFI) and Kelvin-Helmholtz instability are studied when the finite thickness of the inhomogeneous boundary layer is taken into account. The theory of negative energy waves is applied to predict the behavior and interactions of the surface modes in such plasmas. Growth rates of RFIs are examined under various conditions. The dependence of critical velocities on the density ratio is studied under the assumption of a nonuniform magnetic field resulting in different plasma 8 on both sides of the inhomogeneous layer. Possible observational signatures of the RFI are also discussed. (C) 2003 American Institute of Physics. [References: 31]