Influence of the Transport on the Instability of a Boundary Current

Abstract

This paper examines the stability properties of coastal currents having the same potential vorticity (PV) structure but different transports and widths. The PV structure is chosen so as to verify the Charney?Stern necessary condition for instability: two PV fronts associated with opposite sign gradients exist. The authors find that the characteristics of the eddies formed by the current are sensitive to the transport and current width, and very different vortex sizes can be obtained when varying the latter parameters. The diameter is indeed shown to diminish when increasing the transport or diminishing the current width. Analytical and numerical results also show that there are parameter ranges for which the current is stable, and that the Charney?Stern criterion is indeed not a sufficient condition for instability. Large transports are, however, necessary to stabilize the current. The model is then used to study the dynamics of a current subject to adiabatic changes, and a few scenarios are reviewed. In particular, the authors explain how eddies with different diameters can be generated from the same current.