Kelvin–Helmholtz instability in an unstable layer of finite-thickness

Three-dimensional MHD simulations of Kelvin–Helmholtz instability (KHI) have been performed to investigate its relevance to the magnetotail-flank situation. The stabilization effect of the intense lobe magnetic field can be a crucial factor that has not been considered. To assess this effect we have studied how the mode grows in an unstable layer of finite thickness (the plasma sheet) sandwiched between stable regions (the lobe in the two-hemispheres). The condition on the magnetosheath side is set in the favorable range for KHI. Results from the two basic configurations studied here suggest that KHI grows vigorously as long as the unstable layer is thicker than a half of the wavelength. The results imply that the condition on the magnetospheric side for KHI to be an important element of the tail-flank dynamics can be met rather easily under northward IMF.