Eddy-Driven Buoyancy Gradients on Eastern Boundaries and Their Role in the Thermocline

Journal Article · Wed Jul 01 00:00:00 EDT 2009 · Journal of Physical Oceanography

DOI:https://doi.org/10.1175/2009jpo4063.1· OSTI ID:1564671

Cessi, Paola ^[1]; Wolfe, Christopher L. ^[1]

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1. Univ. of California, San Diego, CA (United States)

It is demonstrated that eddy fluxes of buoyancy at the eastern and western boundaries maintain alongshore buoyancy gradients along the coast. Eddy fluxes arise near the eastern and western boundaries because on both coasts buoyancy gradients normal to the boundary are strong. The eddy fluxes are accompanied by mean vertical flows that take place in narrow boundary layers next to the coast where the geostrophic constraint is broken. These ageostrophic cells have a velocity component normal to the coast that balances the geostrophic mean velocity. It is shown that the dynamics in these thin ageostrophic boundary layers can be replaced by effective boundary conditions for the interior flow, relating the eddy flux of buoyancy at the seaward edge of the boundary layers to the buoyancy gradient along the coast. These effective boundary conditions are applied to a model of the thermocline linearized around a mean stratification and a state of rest. The linear model parameterizes the eddy fluxes of buoyancy as isopycnal diffusion. Furthermore, the linear model produces horizontal gradients of buoyancy along the eastern coast on a vertical scale that depends on both the vertical diffusivity and the eddy diffusivity. The buoyancy field of the linear model agrees positively with the mean state of an eddy-resolving computation. Because the east–west difference in buoyancy is related to the zonally integrated meridional velocity, the linear model successfully predicts the meridional overturning circulation.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Univ. of California, San Diego, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: FG02-01ER63252
• OSTI ID: 1564671
• Journal Information: Journal of Physical Oceanography, Journal Name: Journal of Physical Oceanography Journal Issue: 7 Vol. 39; ISSN 0022-3670
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Boundary conditions
Buoyancy
Fluxes
Model evaluation/performance
Thermocline