Instability of Meridional Baroclinic Currents*

Abstract

Abstract The baroclinic instability of a meridional current in a north–south channel is investigated in a two-layer model for the case when the current has no horizontal shear. The vertical shear of the current provides a potential vorticity gradient in the zonal direction while the beta effect provides a potential vorticity gradient in the meridional direction. The normal modes of the two-layer baroclinic flow are found both numerically and analytically. In contrast to the situation when the current is in the zonal direction there seems to be no minimum shear required for instability in spite of the active presence of the planetary vorticity gradient, β, although the growth rates of the instability are reduced as the shear is weakened. Also, the horizontal structure of the unstable mode is a strong function of the parameters, and weakly growing modes exhibit a boundary layer structure and are compressed to a narrow region near the western edge of the channel. The unstable modes are connected to the neutr...