OC4331-Sample Topic Page

OC4331-Mesoscale Oceanography
Final Project Summary

Topic Area

Gulf Stream Frontal Eddies

Project Team Member(s)

LT Karen Wingeart, USN

Major Findings

Gulf stream frontal eddies are cold cyclonic features that form in troughs of northward propagating Gulf Stream meanders in the South Atlantic Bight (Figure 1).Ý A deep upwelled cold dome forms along the western edge of the offshore meander and a shallow warm filament extends southward along the shoreward side of the cold dome.Ý Previous studies concluded the following frontal eddy characteristics:

Form downstream of the Charleston Bump
Average size: 150km alongshore by 50 km cross-shore diameter
Average propagation: 24 km/day
Average recurrence: 6 days
Cyclonic circulation extends throughout the water column
Temperature anomaly of cold core is greatest at depth

The Frontal Eddy Dynamics Experiment (FRED) was conducted offshore North Carolina between Cape Fear and Cape Hatteras from May through November 1987.Ý AVHRR Satellite imagery was used to locate frontal eddies.Ý Other measurements taken included shipboard and aircraft XBT/AXBT surveys, acoustic doppler current profiler data, Argos-tracked drifting buoys data, and surface salinity samples.Ý Eddy Abbott was the first and most intensively sampled frontal eddy surveyed (Figure 2).Ý It was tracked from 9-19 May and is the first eddy to be seeded with buoys and tracked past Cape Hatteras.Ý Typical 150m temperatures upstream and downstream of the cold dome were 17°-18°C.ÝThe evolution of Eddy Abbott's passage was as follows:

Warm temperatures and strong down stream flow within the meander crest exist
As cold dome approaches, temperature and alongshore flow decrease greatly
At passage, temperature warms, alongshore flow increases, and cross-shore flow switches from onshore to weaker offshore
After passage, warm downstream alongshore flow occurs in trailing meander crest
Warm filament detaches and remains in Raleigh Bay
Eddy propagates NE past Cape Hatteras and new warm filament develops

FRED experiment concluded that frontal eddies propagate along the North Carolina Coast every 4-5 days and they are associated with small and large mode Gulf Stream meanders.Ý Contrary to previous study results, the North Carolina Shelf is not a graveyard for frontal eddies.Ý Eddy Abbott's cold dome survived past Cape Hatteras.

schematic of Gulf Stream frontal eddy
Figure 1. Typical Gulf Stream frontal eddy formed in meander with warm filament extending shoreward.

Figure 2. AVHRR image of Eddy Abbott located off Cape Fear on 10 May 1987.

References

Glenn, S.M., and C.C. Ebbesmeyer, 1994: "The structure and propagation of a Gulf Stream frontal eddy along the North Carolina shelf break." J. Geophys. Res., Vol. 99, 5029-5046.