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Western Boundary Current Separation Caused by a Deep Countercurrent
Authors:Toshihiro Sakamoto
Institution:Department of Earth and Planetary Science, Graduate School of Science , The University of Tokyo , 7-3-1 Hongo Bunkyo-ku, Tokyo, 113-0033, Japan
Abstract:

It is shown that the deep western boundary current (DWBC) in the North Atlantic may contribute to premature separation of the Gulf Stream. A simple analytical study is made based on the linear barotropic vorticity equation in which a possible effect of the DWBC is introduced as anomalous stretching of the water column in a manner consistent with certain qualitative aspects of the observed features. This additional positive vorticity may be generated by a deep downwelling associated with horizontal shears of the DWBC. It is found that separation latitudes are farther to the south as the stretching is strengthened. Vertical motion required for a southward shift of order unity (e.g., 500 km) is estimated to be of the order of 0.05 mm s m 1 , in reasonable agreement with the observed values. It is suggested that since the DWBC is intimately linked with the thermohaline circulation, a meridional migration of the Gulf Stream separation might reflect long-term variations in the North Atlantic.
Keywords:Boundary Layer Separation  Linear Theory  Barotropic Model  Deep Western Boundary Current  Climate Change
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