Eddy diffusivities in the Southern Ocean from an eddying model

在用于气候预测的模式中，对南大洋涡旋动力学的真实描述至关重要。中尺度涡旋产生的混合被认为在南极环极流（ACC）的水团和示踪剂转移中起重要作用。反过来，这些水质量转移被认为控制着全球翻转环流和海洋间交换。该项目的中心目标是量化南大洋的拉格朗日等压涡旋扩散率，表征其水平和垂直分布，并评估其参数化整个ACC的等压涡旋示踪通量的能力。这些问题将使用Los Alamos国家实验室（LANL）平行海洋计划（POP）的0.1度、42层全球配置来解决。知识价值：在标准气候尺度海洋模式中，南大洋涡旋混合过程的表现存在很大的不确定性。涡旋扩散通常用于参数化涡旋的影响，气候尺度模式对南大洋涡旋扩散系数的大小非常敏感。当使用恒定涡旋扩散系数而不是可变涡旋扩散系数时，海洋环流对地表强迫的敏感性是否会改变尚不清楚，更根本的是，涡旋扩散模式是否充分模拟了局部、甚至纬向综合示踪剂输送。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。不同的方法导致了南大洋震级和空间分布的冲突。拉格朗日浮子提供了一种测试扩散模型适用性的方法。大约10,000个数值浮标将部署在海洋模型中，在ACC内外的不同位置和深度范围内，以估计拉格朗日扩散率及其空间分布。这些拉格朗日扩散系数在参数化纬向综合和局部涡旋示踪剂输送方面的技巧将被评估。这一项目将有助于协调南大洋相互矛盾的扩散率估计，并最终使我们能够评估扩散率的空间结构对准确模拟南大洋涡旋通量有多大影响。更广泛的影响：该项目将有助于博士后研究员的早期职业发展。该研究将探索不同的方法来参数化混合系数，这将在预测气候模型中进行测试。详细评估拉格朗日方法及其与其他方法的涡流通量和扩散率估计的关系，将有助于分析部署在整个海洋上的浮标的数据。特别是，本研究中所研究的方法将有助于解释由180个声学浮标返回的原位数据，这些浮标是美国国家科学基金会资助的南大洋环流和等环流混合实验（DIMES）实验的一部分。该项目是对美国CLIVAR（气候变率和可预测性）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.