Radiating instability of nonzonal ocean currents

Abstract

The linear stability of nonzonal flow, uniform in the alongjet direction on a beta plane, is studied. The flow is balanced by a forcing term in the potential vorticity equation. The problem is analyzed in both barotropic and two-layer models. The stability computations are performed for piecewise constant and continuous velocity profiles. New stability properties of nonzonal jets are discussed. The destabilizing effect of the meridional tilt of the jet is demonstrated. The study focuses on the ability of the current to support radiating instabilities capable of significant penetration into the far field. The radiating properties of nonzonal currents are found to be very different from those of zonal currents. In particular, purely zonal flows do not support radiating instabilities, whereas flows with a meridional component are capable of radiating long waves. The new mechanism for radiation is related to the nonzonality of a current.