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Gulf Stream flow field and events near 68°W

Authors

  • Thomas J. Shay,

  • John M. Bane,

  • D. Randolph Watts,

  • Karen L. Tracey


Abstract

The SYNoptic Ocean Prediction (SYNOP) experiment was designed to provide an accurate understanding of the energetic mesoscale processes in the Gulf Stream. The Central Array measured velocity and temperature throughout the water column, with horizontal extent large enough nearly to span the meander envelope and Eulerian mean structure of the jet at 68°W. The 55- to 70-km mooring spacing resolved mesoscale eddy interactions with the Gulf Stream, and the 26-month duration allowed stable estimation of long-term mean fields. Six steep meander troughs propagated into or developed within the array, each lasting around 30–60 days, thus impressing a small mean trough near 68°W in the predominantly eastward currents at jet level (1000 m and above). At the deep level (3500 m) the mean flow was southwest at the shoreward sites shallower than 4300 m, but it flowed cyclonically around a mean low-pressure anomaly affecting all the deeper offshore sites. The eddy kinetic energy per unit mass (EK) decreased by a factor of about 2.5 with each depth increment from 400 to 700 to 1000 m but was only a factor of 2 smaller at 3500 m than at 1000 m. Values of EK in the upper central jet (400 m) were 100 to 230 mJ kg−1 and were 4–13 mJ kg−1 at 3500 m. Overall, EK in the upper 1000 m at 68°W was higher than previously published values at 55°W. Two extended case studies of meander propagation through the array demonstrate the development and intensification of deep cyclonic and anticyclonic flows beneath the Gulf Stream. The cyclonic flow at 3500 m, associated with amplifying meander troughs, often exceeded 0.35 m s−1, which was much larger than the typical 0.05 m s−1 deep mean velocities.

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