Instability of a Front with a Layer of Uniform Potential Vorticity

Abstract

The linear stability of a front whose lower layer has a uniform potential vorticity is investigated. The results are compared with the unstable modes of a frontal model which consists of two homogeneous flows with an interacting interface. Unstable modes with a phase speed close to the velocity of the basic flow in the lower layer, which exist in the frontal model of two homogeneous flows, are stabilized in the present model. This feature is explained by the absence of Rossby waves in the reduced one-layer problem of the lower layer resulting from the uniformity of its potential vorticity. The results show that the stability of a front is strongly affected by the potential vorticity distribution. Careful attention is needed for the application of the frontal model with uniform potential vorticity, which is a critical situation.