Eddy diffusivities in the Southern Ocean from an eddying model

在用于气候预测的模式中，对南大洋涡动动力学的真实描述是至关重要的。中尺度涡旋产生的混合被认为在南极绕极流(ACC)的水团和示踪物的转移中发挥着重要作用。反过来，这些水质量转移被认为控制着全球颠覆的环流和大洋之间的交换。该项目的中心目标是量化南大洋的拉格朗日等周期涡旋扩散系数，描述它们的水平和垂直分布，并评估它们对整个ACC等周期涡旋示踪通量的参数化能力。这些问题将使用洛斯阿拉莫斯国家实验室(LANL)并行海洋计划(POP)的0.1度、42层全球配置来解决。智力优势：在标准气候尺度海洋模式中，南大洋涡旋混合过程的表示存在很大的不确定性。涡旋的影响通常是用涡旋扩散来参数化的，而气候尺度模式对南大洋涡旋扩散系数的大小非常敏感。当使用恒定的涡旋扩散系数而不是可变的涡旋扩散系数时，海洋环流对表面强迫的敏感性是否会改变，目前尚不清楚，更根本的是，涡旋扩散模型是否充分模拟了当地的、甚至是纬向整合的示踪剂输送也不清楚。一个相关的基本问题是确定涡旋扩散系数的水平和垂直分布。不同的方法在南大洋造成了相互冲突的等级和空间分布。拉格朗日浮动提供了一种检验扩散模型适用性的方法。将在海洋模式中、在行政协调委员会内外的不同位置和在一定深度范围内部署大约10,000个数值浮标，以估计拉格朗日扩散系数及其空间分布。将评估这些拉格朗日扩散系数在参数化纬向积分以及ACC中的局地涡旋示踪输送方面的技能。这个项目将有助于正在进行的协调南大洋扩散系数估计的相互矛盾的努力，并最终使我们能够评估扩散系数的空间结构在准确模拟南大洋涡旋通量方面的重要性。更广泛的影响：该项目将有助于博士后研究人员的早期职业发展。这项研究将探索将混合系数参数化的不同方法，这将在预测气候模型中进行测试。对拉格朗日方法及其与涡流通量和其他方法估计的扩散系数的关系进行详细评估，将有助于对分布在海洋各地的浮标数据进行分析。特别是，这项研究中调查的方法将有助于解释180个声学浮标返回的现场数据，这些浮标是美国国家科学基金会资助的南大洋Diapycna和Isopycna混合实验的一部分。该项目是对美国气候可变性和可预测性(CLIVAR)计划的贡献。

Realistic depiction of Southern Ocean eddy dynamics is critical in models used for climate prediction. Mixing generated by mesoscale eddies is believed to play an important role in the transfer of water masses and tracers across the Antarctic Circumpolar Current (ACC). In turn, these water mass transfers are thought to control the global overturning circulation and inter-ocean exchange. The central goals of this project are to quantify Lagrangian isopycnal eddy diffusivities in the Southern Ocean and to characterize their horizontal and vertical distributions, and to assess their ability to parameterize isopycnal eddy tracer fluxes across the ACC. These questions will be addressed using the 0.1 degree, 42-level global configuration of the Los Alamos National Laboratory (LANL) Parallel Ocean Program (POP).Intellectual Merit: Large uncertainty exists in the representation of Southern Ocean eddy mixing processes in standard climate scale ocean models. The effects of eddies are commonly parameterized using eddy diffusion, and climate scale models are very sensitive to the magnitude of the eddy diffusion coefficients in the Southern Ocean. Whether the sensitivity of the ocean circulation to surface forcing is altered when using constant eddy diffusion coefficients rather than variable eddy diffusion coefficients remains unclear, and, more fundamentally, it is unclear if local, or even zonally integrated tracer transports are simulated adequately by the eddy diffusion model. A related fundamental issue is to determine the horizontal and vertical distributions of the eddy diffusion coefficients. Different methods have resulted in conflicting magnitudes and spatial distributions in the Southern Ocean. Lagrangian floats provide a way to test the applicability of the diffusion model. Of order 10,000 numerical floats will be deployed in the ocean model, at various locations within and outside the ACC and at a range of depth levels to estimate Lagrangian diffusivities and their spatial distributions. The skill of these Lagrangian diffusivities in parameterizing zonally integrated as well as local eddy tracer transport in the ACC will be assessed. This project will contribute to ongoing efforts to reconcile conflicting diffusivity estimates for the Southern Ocean and will ultimately allow us to assess how much the spatial structure of the diffusivities matters in simulating Southern Ocean eddy fluxes accurately.Broader Impacts: The project will contribute to the early career development of a postdoctoral researcher. The research will explore different ways to parameterize mixing coefficients, which will be testable in predictive climate models. A detailed assessment of Lagrangian methods and their relation to eddy fluxes and diffusivity estimates from other methods will benefit efforts to analyze data from floats deployed all over the ocean. In particular, the methods investigated in this study will contribute to the interpretation of in situ data returned by the 180acoustic floats that are being deployed as part of the NSF-funded Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) experiment. This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program.