Eastern-Boundary Contribution to the Residual and Meridional Overturning Circulations
Eastern-Boundary Contribution to the Residual and Meridional Overturning Circulations
复制标题
东边界对剩余和经向翻转环流的贡献
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
B. Ludka
中科院分区：
文献类型：
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作者：
P. Cessi;C. Wolfe;B. Ludka
构造了沿特定层位线性化的温跃层模型和正压线性风驱动的Stommel解。强迫是机械的（表面风应力）和热力学的（表面浮力边界条件）。文中还考虑了大尺度浮力梯度参数化的湍流扩散系数和涡动浮力通量的影响。浮力通量在边界附近特别重要，在那里它们调解进出狭窄的地转下沉/上升流层的运输。这些窄层的动力学可以被地转平衡流的有效边界条件所取代。有效边界条件表明，垂直于有效海岸的残余流消失。单独的欧拉分量和涡流分量可以是非零的。该公式保留了总质量和总浮力，同时允许在下/上升流层内欧拉和输送浮力之间进行交换。反过来，这种交换允许浮力梯度沿着所有固体边界，包括东部边界。特别关注的是东西墙的浮力，因为东西浮力差决定了经向翻转环流。正压流所包含的平流浮力使得经向环流和残余的翻转环流之间有意义的区别，同时保留了线性模型的简单性。经向和纬向的残余流揭示了地下浮力分布是如何建立的，特别是经向浮力梯度是如何在深度上反转的。反过来，水平浮力梯度在经向和残余的倾覆环流中维持堆叠的反向旋转单元。每个单元都给出了定量的尺度论证，表明浮力、风应力、潜流和涡流扩散率以及其他强加的参数是如何影响翻覆强度的。
A model of the thermocline linearized around a specified stratification and the barotropic linear winddriven Stommel solution is constructed. The forcings are both mechanical (the surface wind stress) and thermodynamical (the surface buoyancy boundarycondition). The effects of diapycnal diffusivity and of eddy fluxesofbuoyancy,parameterizedintermsofthelarge-scalebuoyancygradient,areincluded.Theeddyfluxes of buoyancy are especially important near the boundaries where they mediate the transport in and out of the narrow ageostrophic down-/upwelling layers. The dynamics of these narrow layers can be replaced by effective boundary conditions on the geostrophically balanced flow. The effective boundary conditions state that the residual flow normal to the effective coast vanishes. The separate Eulerian and eddy-induced components may be nonzero. This formulation conserves the total mass and the total buoyancy while permitting an exchangebetweentheEulerianandeddytransportofbuoyancy withinthedown-/upwellinglayers.Inturn, this exchange allows buoyancy gradients along all solid boundaries, including the eastern one. A special focus is on the buoyancy along the eastern and western walls since east‐west buoyancy difference determines the meridional overturning circulation. The inclusion of advection of buoyancy by the barotropic flow allows a meaningful distinction between the meridional and the residual overturning circulations while retaining the simplicity of a linear model. The residual flow in both meridional and zonal directions reveals how the subsurface buoyancy distribution is established and, in particular, how the meridional buoyancy gradient is reversed at depth. In turn, the horizontal buoyancy gradient maintains stacked counterrotating cells in the meridional and residual overturning circulations. Quantitative scaling arguments are given for each of these cells, which show how the buoyancy forcing, the wind stress, and the diapycnal and eddy diffusivities, as well as the other imposed parameters, affect the strength of the overturn.