Wind–Current Coupling on the Southern Flank of Georges Bank: Variation with Season and Frequency

Marlene Noble U.S. Geological Survey, Woods Hole, MA 02543

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Bradford Butman U.S. Geological Survey, Woods Hole, MA 02543

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Mark Wimbush University of Rhode Island, Narragansett, RI

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Abstract

Comparison of several years of current observations on the southern flank of Georges Bank with nearby wind data shows that the wind–current coupling is primarily between longshelf wind stress and longshelf current. The strongest wind–currnet coupling occurs in winter, when the water column is homogeneous. The weakest coupling is in late summer and early fall, when the water column is highly stratified. The coherence and transfer coefficient between longshelf wind and longshelf current is highest for periods between 4 and 12 days, decreasing both for longer periods (out to 56 days) and shorter periods (down to 2 days). Models of the wind–current coupling indicate that a highly damped resonance may exist on Georges Bank and that a smaller current response is expected when the water column is stratified. The observations also indicate that the wind-driven currents on Georges Bank are strongly controlled by friction. The near-surface current moves to the right of wind stress and there is a spring–neap modulation of the wind–current transfer coefficient caused by the modulation of the bottom stress associated with the spring–neap tidal cycle. The longshelf current is linearly related to wind stress and responds almost symmetrically to wind forcing.

Abstract

Comparison of several years of current observations on the southern flank of Georges Bank with nearby wind data shows that the wind–current coupling is primarily between longshelf wind stress and longshelf current. The strongest wind–currnet coupling occurs in winter, when the water column is homogeneous. The weakest coupling is in late summer and early fall, when the water column is highly stratified. The coherence and transfer coefficient between longshelf wind and longshelf current is highest for periods between 4 and 12 days, decreasing both for longer periods (out to 56 days) and shorter periods (down to 2 days). Models of the wind–current coupling indicate that a highly damped resonance may exist on Georges Bank and that a smaller current response is expected when the water column is stratified. The observations also indicate that the wind-driven currents on Georges Bank are strongly controlled by friction. The near-surface current moves to the right of wind stress and there is a spring–neap modulation of the wind–current transfer coefficient caused by the modulation of the bottom stress associated with the spring–neap tidal cycle. The longshelf current is linearly related to wind stress and responds almost symmetrically to wind forcing.

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