Equilibration of baroclinic meanders and deep eddies in a gulf stream-typejet over a sloping bottom

Spatiotemporal evolution of a small localized meander on a Gulf Stream-type baroclinically unstable jet over a topographic slope is investigated numer ically using a three-dimensional, primitive equation model. An unperturbed jet is prescribed by a potential vorticity front in the upper thermocline o verlaying intermediate layers with weak isentropic potential vorticity grad ients and a quiscent bottom layer over a positive (same sense as isopycnal tilt) cross-stream continental slope. A series of numerical experiments wit h the same initial conditions over a slope and flat bottom on the beta plan e and on the f plane has been carried out. An initially localized meander evolves into a wave packet and generates dee p eddies that provide a positive feedback for the meander growth. Meanders found growing over a flat bottom are able to pinch off resembling warm and cold core rings, while in the presence of a weak bottom slope such as 0.002 , the maximum amplitudes of meanders and associated deep eddies saturate wi th no eddy shedding. In the flat bottom case, the growth rate is only 10% l arger than in the weak slope case. Nevertheless, the bottom slope efficient ly controls nonlinear saturation of meander growth via constraining the dev elopment of deep eddies. The topographic slope modifies the evolution of de ep eddies and causes the phase displacement of deep eddies in the direction of the upper layer troughs/crests, thus limiting growth of the meanders. B ehind the wave packet peak deep eddies form a nearly zonal circulation that stabilizes the jet in an equilibrated state. The main equilibration mechan ism is a homogenization of the lower-layer potential vorticity by deep eddi es. The width of the homogenized zone is narrower for a larger slope and/or on the beta plane. These results have the following implications to the Gulf Stream dynamics: 1) maximum of the meander amplitudes increase as the topographic slope rela xes in qualitative agreement with observed behavior of the Gulf Stream, 2) the phase locking of the meanders with deep eddies underneath at the nonlin ear stage agrees qualitatively with the observed structure of large amplitu de cyclonic troughs at the central array, and 3) the increase of the barotr opic transport on the warm side of the jet and the generation of the recirc ulation on the cold side of the jet is consistent with observations in the Gulf Stream system downstream of Cape Hatteras.