URI physical oceanographers study how topography affects the Gulf Stream's path


Scientists have been studying the Gulf Stream in the North Atlantic Ocean for centuries but still do not completely understand the swiftly moving current's physical dynamics. One mysterious phenomenon is the path of the Gulf Stream, which does not follow a straight line, but bends, meanders, and changes from day to day. Satellite observations, however, show that sometimes the meandering seizes, and the current flows along a nearly straight line, radically changing its typical behavior. Little is known of what causes this phenomenon.

In a recent issue of the Journal of Physical Oceanography, physical oceanographers Drs. Sergei A. Frolov, Georgi G. Sutyrin, and Isaac Ginis of the University of Rhode Island Graduate School of Oceanography (GSO) examine the structure of the Gulf Stream to identify the conditions under which the current meanders or remains straight. Specifically, the scientists, with a grant from the Office of Naval Research, investigate how the structure of the sea floor affects the Gulf Stream's path.

To simulate the Gulf Stream's behavior numerically, the URI scientists used the Princeton Ocean Model (POM). Originally developed by Alan Blumberg and George Mellor in 1987, POM is widely distributed to the academic community and industry and is run operationally as part of the Coastal Ocean Forecast System at the National Center for Environmental Predictions. With POM, modelers can change the seafloor and other stream parameters to determine how they affect the Gulf Stream's path.

Sutyrin, Ginis, and Frolov's current experiment follows an initial series of computer experiments they conducted in 2001 that began their investigation into how conditions below the Gulf Stream influence the behavior of the current under different topographical conditions. These experiments revealed a new mechanism that causes the current to cease meandering and follow a nearly straight path. It was termed the state of "jet equilibration."

The new analysis reveals that the Gulf Stream in the state of equilibration is associated with counter-currents immediately to the north and to the south of the main current. Interestingly, the northern counter-current is found to be nearly twice as strong as its southern counterpart. This newly discovered feature of the Gulf Stream in the state of equilibration is related to behavior of the deep currents beneath the stream over topographical slopes.

"Even though good qualitative agreement was found between the id ealized numerical experiments and observed real meandering events in the Gulf Stream, the behavior of the real Gulf Stream is certainly more complicated," said Frolov. "In particular, the nonuniform character of the continental shelf between Cape Hatteras and the New England seamounts is expected to affect significantly the meander equilibration stage. Further studies are necessary to investigate the effect of more realistic topography on jet equilibration."

The URI Graduate School of Oceanography is one of the country's largest marine science education programs, and one of the world's foremost marine research institutions. Founded in 1961 in Narragansett, RI, GSO serves a community of scientists who are researching the causes of and solutions to such problems as acid rain, harmful algal blooms, global warming, air and water pollution, oil spills, overfishing, and coastal erosion. GSO is home to the Coastal Institute, the Coastal Resources Center, Rhode Island Sea Grant, the Institute for Archaeological Oceanography, the Pell Marine Science Library, and the National Sea Grant Library.

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