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Free Content Wind-driven secondary circulation in ocean mesoscale

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Abstract:

A two-dimensional, numerical circulation model is used to study the response of a stratified, f-plane ocean current to wind stress forcing at the surface. Nonhydrostatic, primitive equations are integrated on a 3 m vertical and 400 m horizontal grid in a periodic domain perpendicular to the ocean current. Initially, a geostrophically balanced current [Vi(x, z)] with a maximum Rossby number of 0.16–0.8 is maintained against horizontal and vertical diffusion by a body force. A spatially uniform wind is applied along and across this jet. A secondary circulation is created as a result of the nonlinear interaction between the jet and wind-driven flow in the Ekman layer. We present results from seven numerical experiments.

When the wind blows in the direction of the jet (against the jet), a narrow upwelling (downwelling) area and broad downwelling (upwelling) area are formed. This secondary circulation pattern extends well below the mixed layer. When the wind blows perpendicular to the jet, the secondary circulation does not extend below the mixed layer. The fully nonlinear secondary circulation is 50% weaker than the circulation produced by the semi-linearized calculation around the basic state, Vi. Near-inertial fluctuations appear and are confined to the negative relative vorticity side of the circulation (dV/dx < 0). The time-averaged vertical velocity can be as high as 1.5 m/day with a wind stress of 1 dyne/cm2 over a jet and a maximum Rossby number of 0.16. The magnitude of the vertical circulation in this symmetric basic state is dependent on the Rossby number and the horizontal and vertical mixing coefficients.

Document Type: Research Article

DOI: http://dx.doi.org/10.1357/0022240943077037

Publication date: May 1, 1994

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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