A signature of MHD surface wave field-aligned currents in plasmas

Abstract

A MHD surface wave approach to the large-scale field-aligned current (FAC) structure propagation is applied. The FAC structures under study resemble those of three-sheet FAC magnetic field configurations observed in the Earth's magnetosphere. The MHD surface wave magnetic field possesses a three-sheet signature centered at the plasma boundary regions (the middle sheet) where the FAC flows primarily. In general, the non-linear steady-state MHD surface wave magnetic field characteristics around the plasma boundary having a finite thickness are derived. The plasma flow pattern due to the non-linear interaction between the MHD surface wave current and the magnetic field (ambient and wave) is examined, as well, The effects of various factors as initial flow velocity, plasma pressure gradients, ambient magnetic field on the plasma vortex drift structures are considered. The simple well-known dipole vortex structure is revealed provided that the plasma parameters in various regions are equalized, the plasma boundary region degenerates into a non-dimensional separatrix and the corresponding FAC vanishes.