A NUMERICAL-SIMULATION OF THE EVOLUTION AND PROPAGATION OF GULF-STREAM WARM-CORE RINGS

The evolution and propagation of Gulf Stream warm core rings in a flat -bottom, beta-plane ocean are studied using a three-dimensional primit ive equation model. Rings are produced by a heat source that is turned on and off slowly in the upper 750 m of the water column. Besides an anticyclone in the upper ocean, a deep cyclone is generated below the surface eddy. In the first 30 days, the surface anticyclone moves slow ly southwestward because of beta dispersion and vorticity advection. I n waters 4000 m deep, both the anticyclone and the cyclone intensify, and a barotropic vortex pair is formed. The vortex pair moves rapidly southeastward. Its propagation becomes steady and eastward after the c yclone sheds an eddy. The cyclone in the vortex pair moves away from t he ring at the end of 6 months, and both vortices begin to propagate w estward separately. Fluid to a depth of 3000 m, much deeper than that of forcing, is transported by the ring. The formation of a strong vort ex pair is associated with the generation of relative vorticity in bot h vortices by unstable waves of the second azimuthal mode. In strong r ings, the increase in vorticity could produce rapid propagation. Eastw ard propagation is a result of change in planetary vorticity and loss of relative vorticity during cyclone splitting. In waters shallower th an 4000 m, the vortex pair is less stable and more vorticity is lost b y cyclone splitting. There is still a rapid movement toward the south but the eastward propagation is weak. Rings in waters shallower than 4 000 m are likely to remain on the continental slope off the U.S. East Coast and induce large amounts of momentum and mass transfer over the continental margin.