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Particularly clear skies for the Gulf Stream

Jan 1, 2003

Particularly clear skys for October allowed analysts to track an unusual feature of the Gulf Stream. Presumably unnoticed by mariners on their way to the Caribbean or to points along the U.S. East Coast was a large warm eddy located south, yes south of the Gulf Stream.

Typically, warm-core eddies are found north of the Gulf Stream while cold-core eddies are found south of the stream. Most Bermuda sailors are familiar with the ways of warm eddies spinning clockwise and cold eddies spinning counterclockwise.

This past fall, however, Gulf Stream charts such as the one shown with this column by Jenifer Clark have exhibited a conspicuously marked ring of warm water in the vicinity of 36° N, 64° W, well south of the main body of the stream. This anomalous, clockwise warm eddy was moving slowly to the west and southwest throughout October and November.

"We are aware of the existence of maybe half a dozen of these each year," said Clark, who provides Gulf Stream data and analysis as a business service. "But during periods of particularly clear weather we may be seeing that these anomalous eddies are out there all the time," she added.

"We're not really sure how these eddies originate because they don't seem to break off from meanders of the stream in the normal way," said Clark. "I think there are dynamics involved which we don't really understand yet."

Gulf Stream observations are made using infrared satellite imagery. When there is cloud cover it blocks the satellite's view of the ocean surface.

Oceanographers have explained that anomalous eddies typically exist in conjunction with a normally rotating eddy, often with water between them entrained into motion. In this case, the accompanying eddy might be a cold eddy located just to the southeast at 36° N, 62° W. A pair of such eddies is typically known as a double vortex. The phenomenon of double-vortex eddies has been observed in many oceanic locations and can be simulated in any body of water, including a bathtub.

"This particular warm eddy may last for as long as six months," said Clark. "I don't think it is going to be entrained by the main body of the Gulf Stream, and since it is warm and south of the Gulf Stream it's not likely to sink beneath the surface the way many cold eddies do. It looks pretty stable, and it's been there for a while."

Those interested in more information can contact Jenifer Clark's Gulf Stream at 301-952-0930.


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