Scalings for eddy buoyancy transfer across continental slopes under retrograde winds
Scalings for eddy buoyancy transfer across continental slopes under retrograde winds
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逆行风下大陆坡涡流浮力传递的尺度
DOI：
10.1016/j.ocemod.2020.101579
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发表时间：
2020
期刊：
影响因子：
3.2
通讯作者：
Stewart, Andrew L.
中科院分区：
文献类型：
--
作者：
Wang, Yan;Stewart, Andrew L.
斜压涡旋再层化强烈地影响着海洋的大气环流和示踪收支，在粗分辨率海洋气候模式中通常通过Gent-McWilliams(GM)方案进行参数化。通过使用涡旋解析模拟和理论发展对GM涡旋传递系数进行了改进，这些参数化得到了改进。然而，以前的努力主要集中在开阔的海洋，现有的全球模式参数化法对大陆斜坡的适用性仍有待解决。在这项研究中，我们使用一套涡旋分辨的、面向过程的模拟来测试在模拟大陆斜压湍流时，涡浮力扩散率、平均流动特性和地形几何之间的比例关系。我们集中在逆风(即与地形波传播方向相反的)风的情况下，这是一种常见的出现在副热带气旋边缘的构型。Jansen等人最近测试的基于混合长度理论(MLT)的标度。(2015)在平坦的海床上拍摄。本文强调了局部坡度参数在控制非线性涡浮通量中的重要作用。几何框架和CF尺度都可以再现沿海岸均匀的大陆坡面上的深度平均涡流浮力输送，只要选择适当的恒定前置因子。在大陆斜率和开阔海洋环境中推广这些比例，需要通过经验推导的分析函数引入依赖于当地斜率参数的前置因素。相反，当采用恒定的预因子时，基于MLT的尺度不能量化沿海岸均匀的陆坡上的涡浮力输送，但当预因子通过局部斜率参数的经验函数进行调整时，它可以再现横坡涡通量。这些尺度在预测海洋模拟中的应用还取决于与大陆斜坡地形波纹相关的站立涡旋的准确表示。这些发现为扩展现有的参数化瞬变涡旋的方法提供了基础，并呼吁未来努力在粗分辨率海洋气候模式中参数化站立涡旋。
Baroclinic eddy restratification strongly influences the ocean’s general circulation and tracer budgets, and has been routinely parameterized via the Gent–McWilliams (GM) scheme in coarse-resolution ocean climate models. These parameterizations have been improved via refinements of the GM eddy transfer coefficient using eddy-resolving simulations and theoretical developments. However, previous efforts have focused primarily on the open ocean, and the applicability of existing GM parameterization approaches to continental slopes remains to be addressed. In this study, we use a suite of eddy-resolving, process-oriented simulations to test scaling relationships between eddy buoyancy diffusivity, mean flow properties, and topographic geometries in simulations of baroclinic turbulence over continental slopes. We focus on the case of retrograde (i.e., opposing the direction of topographic wave propagation) winds, a configuration that arises commonly around the margins of the subtropical gyres.Three types of scalings are examined, namely, the GEOMETRIC framework developed by Marshall et al. (2012), a new ”Cross-Front” (CF) scaling derived via dimensional arguments, and the mixing length theory (MLT)-based scalings tested recently by Jansen et al. (2015) over a flat ocean bed. The present study emphasizes the crucial role of the local slope parameter, defined as the ratio between the topographic slope and the depth-averaged isopycnal slope, in controlling the nonlinear eddy buoyancy fluxes. Both the GEOMETRIC framework and the CF scaling can reproduce the depth-averaged eddy buoyancy transfer across alongshore-uniform continental slopes, for suitably chosen constant prefactors. Generalization of these scalings across both continental slope and open ocean environments requires the introduction of prefactors that depend on the local slope parameter via empirically derived analytical functions. In contrast, the MLT-based scalings fail to quantify the eddy buoyancy transfer across alongshore-uniform continental slopes when constant prefactors are adopted, but can reproduce the cross-slope eddy flux when the prefactors are adapted via empirical functions of the local slope parameter. Application of these scalings in prognostic ocean simulations also depends on an accurate representation of standing eddies associated with the topographic corrugations of the continental slope. These findings offer a basis for extending existing approaches to parameterizing transient eddies, and call for future efforts to parameterize standing eddies in coarse-resolution ocean climate models.
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影响因子：
2.8
作者：
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