A simulation and theoretical study of energy transport in the event of MHD Kelvin-Helmholtz instability

Surface waves developed from the Kelvin-Helmholtz (K-H) instability perturb the ambient plasma and radiate waves that extract surface-wave energy. In magnetohydrodynamic (MHD) plasma, the fast-mode waves can propagate across the magnetic field lines. The fast-mode waves emitted from the surface perturbations should play an important role in transporting the surface-wave energy away from the velocity shear layer. Thus, the energy transported by the K-H instability should not be confined near the velocity shear layer. In this study, energy transport in the events of K-H instabilities is studied by the two-dimensional MHD simulation. Our simulation results indicate that most of the energy flux is confined in the vicinity of the velocity shear layer when the fast-mode Mach number of the surface wave is less than one. However, a small amount of the surface-wave energy is transported away from the velocity shear layer by the fast-mode waves. A considerable amount of the surface-wave energy is transported away from the velocity shear layer with the expanding of the fast-mode Mach-cone-like plane waves when the fast-mode Mach number of the surface wave is greater than one. It is shown that the fast-mode Mach-cone-like plane waves can transport the surface-wave energy away from the velocity shear layer efficiently. In this study, we also find that the energy transport velocity obtained from our simulation results is approximately equal to the group velocity of the fast-mode wave. Applications of our simulation results to the magnetosphere are also discussed.