A numerical study of Gulf Stream meandering and associated physical processes

The symmetry properties of the Gulf Stream (GS) system downstream of Cape Hatteras are investigated in a series of idealized numerical experiments. A baroclinically unstable GS-type jet is shown to stabilize over a sloping bottom due to a nearly barotropic shear associated with two recirculation gyres forming north and south of the jet. The recirculation gyres are formed via the mechanism of deep potential vorticity mixing by the bottom-intensified eddies, which accompany the meandering process of the jet. The magnitude of the northern recirculation gyre, as measured by its transport, is larger than the magnitude of the southern recirculation gyre. The 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 density and velocity structure of the GS in steep meanders have been analyzed numerically using the assumption of potential vorticity conservation along the stream. The presented analysis has predicted variations of the density and velocity structure along the stream which are in accord with observations. The force balance in steep meanders has also been analyzed by explicitly excluding various terms from the equations of balance.; A procedure has been developed for the GS initialization in numerical models. The procedure is based on the property of along-stream conservation of the PV structure in the GS. Using the stream PV structure instead of its density or velocity allows for better representation of well developed meanders and situations where GS rings are located close to the Stream.