A stability analysis of the coupled ocean-atmosphere will be presented which shows that the potential energy of the upper layer of the ocean is available to generate growing planetary waves through an upward transfer of energy across the sea surface, which is accomplished by the rate of working of the sea surface displacement wave. On considering a two and a half layer model consisting of an atmospheric planetary boundary layer, coupled with a two layer ocean comprising an active upper layer and a lower layer in which the velocity pertubation is zero, we find that coupled unstability can occur in regions of the ocean, where the winds are Westerlies, and the upper layer ocean current is westward relative to the lower layer. The unstable wave is a divergent Rossby wave, which is steered by the zonal wind velocity, and has a wavelength of about 6000 km, and propagates eastward at the speed of the deep ocean current.

It is proposed that this instablity, which has a multidecadal growth time constant, may be generated in the Southern Ocean, and that its properties are similar to observations of the Antarctic Circumpolar Wave.