STABILITY OF A WESTERN BOUNDARY CURRENT WITH CURVATURE

The linear stability of an idealized western boundary current is studi ed with the emphasis on the effect of curvature. The barotropic quasig eostrophic vorticity equation is modified to incorporate the effect of small curvature. For eastward flow, the curvature increases the growt h rate of the unstable mode that has the peak of the eigenfunction on the offshore side of the flow axis, while the growth rate of the unsta ble mode with its peak on the onshore side of the flow decreases. The curvature is found to shift the phase of the unstable waves, resulting in a change of the Reynolds stress, and a consequent change of the gr owth rate. The positive curvature enhances the dependence of the criti cal Reynolds number on the flow orientation. For the flow that has zer o velocity on the coast, the cyclonic curvature is found to decrease t he critical Reynolds number when the jet is northeastward.