Surface waves and field-aligned currents in the magnetosphere

Abstract

The Kelvin-Helmholtz instability on the magnetopause is one of the MHD surface wave (SW) events encountered in the magnetosphere. The cusp and plasmasheet regions consist of one or two plasma discontinuities with steep boundaries. As a result of the plasma structuring a propagation of MHD surface waves to the Earth is supported. This point is illustrated by an analysis of the polarization of MHD surface waves propagating along a plasma layer and an ambient magnetic field B parallel to the interfaces. In the general case the polarization of the MHD surface waves in the plane transverse to the magnetic field B is elliptical. An essential feature in the polarization of the MHD surface modes is the presence of jumps in the magnetic disturbance component b t at the interfaces. The b t component jump is interpreted as SW field-aligned current (FAC) flowing at the boundary. The surface wave MHD approach is applied to large-scale FAC in the magnetosphere. Non-linear zero-frequency MHD surface wave magnetic field characteristics around the plasma boundary of finite thickness are derived. The plasma flow pattern due to the non-linear interaction between the MHD surface wave FAC current and the magnetic field (ambient and wave) is examined, as well. Effects of various factors as initial flow velocity, plasma pressure gradients, ambient magnetic field on the plasma vortex structures in the magnetosphere are considered