Rotating magnetohydrodynamic free-shear flows. I. Linear stability analysis

The results of a study are presented of the linear stability of a magnetohydrodynamic planar free-shear flow subject to system rotation and a uniform magnetic field which are both parallel or antiparallel to the shear flow vorticity vector. The results show that, with anticyclonic rotation, the effect of the uniform magnetic field is to enlarge the unstable region of the rotating shear flow, while the growth rate of the most unstable disturbance is left unchanged. With cyclonic rotation, on the other hand, the effect of the magnetic field is to strongly stabilize the flow. The spatial structure of the anticyclonic magnetic shear/Coriolis instability mode is investigated. Considering the Rossby number at which the spatial extent of the most unstable disturbance becomes minimum, it is found that this Rossby number decreases as the uniform magnetic field is intensified.