Dynamics of Gulf Stream Meanders and Frontal Eddies in the South Atlantic Bight.

As the Gulf Stream flows along the outer edge of the southeastern United States' continental shelf, it meanders on and offshore creating frontal eddies which influence the exchange of water between the shelf and the adjacent Atlantic Ocean on weekly time scales. The dynamics controlling the development of such features in this region, the "South Atlantic Bight", were investigated. Analyses of the low-frequency low-wavenumber behavior of the Gulf Stream front revealed two modes of meandering which have maximum amplitudes in the vicinity of the Charleston Bump and periods of a few months to a year. In the southern one-third of the SAB, these modes have small amplitudes and the frontal fluctuations are predominantly due to the meander/frontal eddy processes. The Princeton Ocean Model was tuned for conditions which prevail in the southern South Atlantic Bight and idealized numerical simulations of Gulf Stream meanders and associated frontal eddies were performed. The system was found to be sensitive to both the amplitude and period of a small perturbation applied at the southern boundary and a case which produced events most similar to those observed in nature was studied in detail. The energetics indicate that the development of these features is controlled by a mixture of both baroclinic and barotropic instabilities of the mean Gulf Stream flow. The corresponding momentum balances are equally complex. While the along-isobath flow is predominantly in geostrophic balance, several of the nonlinear advection terms in both horizontal momentum equations play important roles in the space-time development of the flow. In particular, the vertical advection of horizontal momentum as well as frictional dissipation are now recognized as important contributors to the dynamical balances in the vicinity of the steep continental slope.