Dynamically consistent parameterization of mesoscale eddies. Part III: Deterministic approach
Dynamically consistent parameterization of mesoscale eddies. Part III: Deterministic approach
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中尺度涡流的动态一致参数化。
DOI：
10.1016/j.ocemod.2018.04.009
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发表时间：
2018
期刊：
影响因子：
3.2
通讯作者：
Berloff P
中科院分区：
文献类型：
--
作者：
Berloff P
本文继续发展非涡旋和允许涡动海洋环流模式中描述中尺度涡旋效应的动力一致性参数化方法，并着重研究经典的双涡旋问题，其中主要的动力涡旋效应通过涡后向散射机制维持西边界流及其邻近再环流区的东向喷流扩展。尽管这一机制很重要，但人们对它的了解仍然很少，在本文中，我们首先对其进行研究，然后提出并测试其新的参数化方法。我们首先将参考涡旋分辨流动解分解为由空间滤波而不是雷诺分解定义的大尺度和涡流分量。其次，我们发现东向急流及其再环流不仅强健地存在于大尺度气流本身中，而且还存在于经修正的时间平均涡旋以及由横跨瞬时东向急流核心的对号位涡异常的高度各向异性条带构成的瞬变修正涡旋分量中，这是其持续放大的原因。通过一种新的重新映射方法将暂态整流分量从流动中分离出来。我们假设，上述三个东向急流分量最终是由小尺度瞬变涡旋强迫通过涡后向散射机制驱动的，而不是由平均涡旋强迫和大尺度非线性驱动的。我们通过逐步降低后向散射和观察诱发的流动异常来验证这一假设。后向散射分析导致我们形成了关键的涡参数化假设：在涡流允许的模式中，至少部分可分辨的涡后向散射可以被显着放大以改善流动解。这种放大是一种简单而新颖的涡参数化框架，它是通过单参数控制的局部确定性流动粗糙来实现的。通过对原始模式的非涡旋修正和允许涡动修正两个层次的数值模拟，证明了该方法对于恢复东向急流延伸及其邻近的回流区是非常有效的。新的确定性参数化框架不仅具有显著的简单性和良好的性能，而且是动态透明的，因此，它为常见的涡旋扩散和新兴的随机参数化提供了一种强有力的替代方案。
This work continues development of dynamically consistent parameterizations for representing mesoscale eddy effects in non-eddy-resolving and eddy-permitting ocean circulation models and focuses on the classical double-gyre problem, in which the main dynamic eddy effects maintain eastward jet extension of the western boundary currents and its adjacent recirculation zones via eddy backscatter mechanism. Despite its fundamental importance, this mechanism remains poorly understood, and in this paper we, first, study it and, then, propose and test its novel parameterization.We start by decomposing the reference eddy-resolving flow solution into the large-scale and eddy components defined by spatial filtering, rather than by the Reynolds decomposition. Next, we find that the eastward jet and its recirculations are robustly present not only in the large-scale flow itself, but also in the rectified time-mean eddies, and in the transient rectified eddy component, which consists of highly anisotropic ribbons of the opposite-sign potential vorticity anomalies straddling the instantaneous eastward jet core and being responsible for its continuous amplification. The transient rectified component is separated from the flow by a novel remapping method. We hypothesize that the above three components of the eastward jet are ultimately driven by the small-scale transient eddy forcing via the eddy backscatter mechanism, rather than by the mean eddy forcing and large-scale nonlinearities. We verify this hypothesis by progressively turning down the backscatter and observing the induced flow anomalies.The backscatter analysis leads us to formulating the key eddy parameterization hypothesis: in an eddy-permitting model at least partially resolved eddy backscatter can be significantly amplified to improve the flow solution. Such amplification is a simple and novel eddy parameterization framework implemented here in terms of local, deterministic flow roughening controlled by single parameter. We test the parameterization skills in an hierarchy of non-eddy-resolving and eddy-permitting modifications of the original model and demonstrate, that indeed it can be highly efficient for restoring the eastward jet extension and its adjacent recirculation zones.The new deterministic parameterization framework not only combines remarkable simplicity with good performance but also is dynamically transparent, therefore, it provides a powerful alternative to the common eddy diffusion and emerging stochastic parameterizations.
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