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LCDRWayne L Plager, USN

Gulf Stream frontal eddies are defined as the cold cyclonic circulation features formed in the troughs of the northward propagating Gulf Stream meanders in the South Atlantic Bight. The fully developed temperature structure consists of a deep upwelled cold dome along the west wall of the offshore meander, and a shallow warm filament extending from the leading meander crest southward along the shoreward side of the cold dome. The Frontal Eddy dynamics experiment was conducted offshore North Carolina in 1987 with intensive surveys of frontal eddies using satellite imagery, expendable bathythermographs, moored current meters, and drifting buoys. One particular feature, Eddy Abbot was extensively surveyed and tracked. The surface circulation and the propagation characteristics of Eddy Abbott were calculated using a numerical model based upon the buoy trajectories. Prior to this study frontal eddies were assumed to be sheared apart as they approached the confining topography of Cape Hatteras. Eddy Abbot was the first such feature to be tracked past Cape Hatteras and showed that frontal eddies can continue to propagate with the Gulf Stream meander downstream into the Atlantic. Eddy Abbot showed that the cold dome actually accelerates past the confining topography of Cape Hatteras and reaches speeds of up to 70 km/day. The warm filament that is initially associated with the formation of the cold dome travels northwest into Raleigh Bay and is eventually stranded as the cold dome is propagated past Raleigh Bay and no longer can supply warm surface water. Eddy Abbot showed a distinctive time series current meter record, which included a velocity reversal due to the cyclonic circulation of the cold dome. This allowed for the analysis of the long term time record of current meter moorings to conclude that Gulf Stream frontal eddies have a recurrence interval of 4-5 days. The long term studies also revealed two types of frontal eddies, dependent upon the bimodal character of the amplitude of the Gulf Stream meanders. During the small-meander mode, the gulf Stream front is located close inshore along the 100-m isobath and the small warm filaments associated with the frontal eddies rarely penetrate beyond the mid-shelf. During the large meander mode the Gulf Stream front is located farther offshore and the larger warm filaments often penetrate onto the inner shelf.

Glenn, Scott M., Ebbesmeyer, Curtis C., 1994: "The Structure and propagation of a Gulf Stream frontal eddy along the North Carolina shelf break." J. Geophys. Res., Vol. 99, 5029-5045.

Glenn, Scott M., Ebbesmeyer, Curtis C., 1994: "Observations of Gulf Stream frontal eddies in the vicinity of Cape Hatteras." J. Geophys. Res., Vol. 99, 5047-5055.