Parameterization of Frontal Symmetric Instabilities. I: Theory for Resolved Fronts
Parameterization of Frontal Symmetric Instabilities. I: Theory for Resolved Fronts
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DOI：
10.1016/j.ocemod.2016.12.003
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发表时间：
2017
期刊：
影响因子：
3.2
通讯作者：
S. Bachman;B. Fox‐Kemper;John R. Taylor;L. Thomas
中科院分区：
文献类型：
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作者：
S. Bachman;B. Fox‐Kemper;John R. Taylor;L. Thomas
本文提出了一种参数化方法来处理对称不稳定性对分解锋的影响。参数化依赖于表面浮力损失和/或下锋面风的外部强迫，这会降低位涡（PV）并导致有利于SI的条件。参数化由三部分组成。第一部分是垂直涡动粘度的规范，它源自科里奥利力和雷诺动量通量（湍流埃克曼平衡）平衡产生的指定非地转环流，以及之前提出的垂直结构函数。地转剪切产生。涡动粘性的垂直结构被构造成以与解析SI一致的速率提取锋面的平均动能。参数化的第二部分表示近地面对流层，其深度由之前提出的多项式方程确定。参数化的第三部分表示通过小尺度剪切不稳定性和SI的扩散示踪剂混合。用湍流Prandtl数将扩散系数的非绝热垂直分量设定为与涡动粘度成正比，用各向异性扩散系数张量表示沿等密度方向的示踪剂混合。用一组理想化模式对参数化进行初步检验，结果表明，锋面总能量的提取与SI分辨大涡模拟的结果一致，同时产生混合层分层、动量、和位涡廓线，这些廓线与现有边界层参数化的廓线相比是有利的（Large等人，1994年）。新的参数化也表明，以改善垂直混合的被动示踪剂在LES。
A parameterization is proposed for the effects of symmetric instability (SI) on a resolved front. The parameterization is dependent on external forcing by surface buoyancy loss and/or down-front winds, which reduce potential vorticity (PV) and lead to conditions favorable for SI. The parameterization consists of three parts. The first part is a specification for the vertical eddy viscosity, which is derived from a specified ageostrophic circulation resulting from the balance of the Coriolis force and a Reynolds momentum flux (a turbulent Ekman balance), with a previously proposed vertical structure function for the geostrophic shear production. The vertical structure of the eddy viscosity is constructed to extract the mean kinetic energy of the front at a rate consistent with resolved SI. The second part of the parameterization represents a near-surface convective layer whose depth is determined by a previously proposed polynomial equation. The third part of the parameterization represents diffusive tracer mixing through small-scale shear instabilities and SI. The diabatic, vertical component of this diffusivity is set to be proportional to the eddy viscosity using a turbulent Prandtl number, and the along-isopycnal tracer mixing is represented by an anisotropic diffusivity tensor.Preliminary testing of the parameterization using a set of idealized models shows that the extraction of total energy of the front is consistent with that from SI-resolving LES, while yielding mixed layer stratification, momentum, and potential vorticity profiles that compare favorably to those from an extant boundary layer parameterization (Large et al., 1994). The new parameterization is also shown to improve the vertical mixing of a passive tracer in the LES.