Parameterization of eddy fluxes based on a mesoscale energy budget
Parameterization of eddy fluxes based on a mesoscale energy budget
复制标题
基于中尺度能量收支的涡流参数化
DOI：
10.1016/j.ocemod.2015.05.007
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发表时间：
2015
期刊：
影响因子：
3.2
通讯作者：
I. Held
中科院分区：
文献类型：
--
作者：
M. Jansen;A. Adcroft;R. Hallberg;I. Held
最近有人提出在海洋模式中建立基于中尺度涡动动能(EKE)预算的涡流扩散系数。在给定合适的长度尺度下，基于混合长度理论，中尺度EKE可以用来估算涡旋扩散率。本文讨论了与EKE预算和混合长度公式相关的一些未解决的问题，并提出了一种改进的基于能量预算的中尺度涡旋扩散系数的参数化方法。采用一种具有二次底阻力的理想平底β平面流道布局，进行了一系列的数值模拟。结果强调了混合长度公式的重要性，以及中尺度EKE的底层特征公式的重要性，这对确定EKE的耗散率是重要的。在行星涡度梯度消失的极限下，混合长度最终由底部阻力控制，但正压湍流理论预测的摩擦停止尺度需要修正以考虑斜压性的影响。任何显著的行星涡度梯度β都会抑制混合，并将有效混合长度限制在莱茵河尺度内。虽然EKE仍然受到底部摩擦的抑制，但EKE的底部特征随着适当的无量纲化摩擦的增加而减小，这与正压湍流相比，显著减弱了底部摩擦变化的影响。因此，对于底摩擦力的适度变化，涡通量可以用Hold和Larichev(1996)提出的忽略底摩擦力影响的标度关系很好地近似。
It has recently been proposed to formulate eddy diffusivities in ocean models based on a mesoscale eddy kinetic energy (EKE) budget. Given an appropriate length scale, the mesoscale EKE can be used to estimate an eddy diffusivity based on mixing length theory. This paper discusses some of the open questions associated with the formulation of an EKE budget and mixing length, and proposes an improved energy budget-based parameterization for the mesoscale eddy diffusivity. A series of numerical simulations is performed, using an idealized flat-bottomedβ-plane channel configuration with quadratic bottom drag. The results stress the importance of the mixing length formulation, as well as the formulation for the bottom signature of the mesoscale EKE, which is important in determining the rate of EKE dissipation. In the limit of vanishing planetary vorticity gradient, the mixing length is ultimately controlled by bottom drag, though the frictional arrest scale predicted by barotropic turbulence theory needs to be modified to account for the effects of baroclinicity. Any significant planetary vorticity gradient,β, is shown to suppress mixing, and limit the effective mixing length to the Rhines scale. While the EKE remains moderated by bottom friction, the bottom signature of EKE is shown to decrease as the appropriately non-dimensionalized friction increases, which considerably weakens the impact of changes in the bottom friction compared to barotropic turbulence. For moderate changes in the bottom-friction, eddy fluxes are thus reasonably well approximated by the scaling relation proposed by Held and Larichev (1996), which ignores the effect of bottom friction.
影响因子：
5.2
作者：
Klocker, Andreas;Marshall, David P.
通讯作者：
Marshall, David P.