Waves and stability of flowing solar wind structures in the framework of the Hall magnetohydrodynamics

Now it is well established that the solar atmosphere, from photosphere to the corona and the solar wind is a highly structured medium. Satellite observations have confirmed the presence of steady flows. Bulk motions are registered along the magnetic field lines which outline the magnetic structures. Recent observations made by two HELIOS spacecrafts have revealed fine structures in high-speed solar wind flows. These structures are in the form of thin flowing layers (or tubes) that are adjacent to each other with differences in their plasma parameters (density, magnetic field, steady flow speed). These structures can be separated by tangential discontinuities in the magnetic filed, across which the total pressure is continuous. Here, we investigate the parallel propagation of magnetohydrodynamic (MHD) surface waves traveling along an ideal flowing plasma slab surrounded by flowing plasma environment in the framework of the Hall magnetohydrodynamics. The magnetohydrodynamics with Hall effect (Hall MHD) gives a fluid description of magnetized plasmas taking into account scales of the order of the ion inertial length, lHall = c/ωpi, at which the dynamics of ions and electrons separates and the medium becomes dispersive. The magnitudes of the plasma densities and flow velocities inside and outside the slab are different. In general, flows increase the waves' phase velocities compared to their magnitudes in a static Hall-MHD plasma slab. Moreover, the plasma flows may cause the triggering of the Kelvin--Helmholtz instability. It turns out that the growth rates of the two kind of surface wave modes that can propagate, notably sausage and kink ones, for a given pair of Alfvenic Mach numbers (inside and outside the jet) are rather similar. In both cases the instability occurs at relatively short wavelengths, i.e., beyond some critical wave numbers