Asymmetry of an Equilibrated Gulf Stream–Type Jet over Topographic Slope

Abstract

The symmetry properties of the Gulf Stream–type jet equilibrated over topographic slope are investigated in a series of idealized numerical experiments. A baroclinically unstable zonal jet equilibrates over a sloping bottom through the process of potential vorticity (PV) homogenization underneath the main thermocline by the bottom-intensified eddy activity associated with the stream meandering. Potential vorticity homogenization underneath the main thermocline leads to formation of recirculation gyres on both sides of the jet. The magnitude of the northern recirculation gyre, as measured by its westward transport, is larger than the magnitude of the southern recirculation gyre. This asymmetry in recirculations is shown to be the result of an asymmetric PV mixing underneath the thermocline produced by an asymmetric jet. In particular, the lateral shift of the velocity maximum near the surface relative to the velocity maximum at depth is shown to be responsible for the asymmetry. The results are related to the Gulf Stream data between 73° and 65°W.