Global MHD simulation of the Kelvin-Helmholtz instability at the magnetopause for northward interplanetary magnetic field

The Kelvin-Helmholtz (K-H) instability is found to occur at the low-latitude magnetopause through global magnetohydrodynamic simulations during a period of northward interplanetary magnetic field. The simulation results present the global picture of the nonlinear evolution of the K-H instability at the magnetopause. At the low-latitude boundary layer (within the latitude of about 30), vortices are generated by the K-H instability at the dayside magnetopause and transported to the far distant magnetotail region along the flank of the magnetosphere; two modes of surface waves propagate along the inner and outer edge of the magnetopause boundary layer, respectively, from the initial point to the tail region; the wavelengths of the inner and outer modes are estimated to vary from 1 to 8 RE as the longitude increases. The vortices are initiated at a longitude of about 28 relative to the Sun-Earth line in the equatorial plane, and their evolution along the magnetopause boundary is studied in detail. We present the characteristics of the inner and outer mode suface waves near the magnetopause boundary layer and find different behaviors of the fast-mode surface waves on the two sides of the magnetopause boundary: the variations of the density and the magnetic field strength of the quasi-fast mode waves are in phase on the magnetosphere side (inner mode), while they are out of phase on the magnetosheath-side (outer mode). The obtained period of the surface waves coincides with the generation period of the vortex at the dayside magnetopause, which is considered to be the intrinsic period of the magetopause for the corresponding interplanetary condition.