Eddy diffusivities in the Southern Ocean from an eddying model

对南大洋涡旋动力学的真实描述在气候预测模式中至关重要。中尺度涡旋产生的混合被认为在南极绕极流（ACC）的水团和示踪剂的传输中起着重要的作用。反过来，这些水的质量转移被认为控制着全球翻转环流和大洋间交换。该项目的主要目标是量化南大洋的拉格朗日等密度涡动扩散系数，并描述其水平和垂直分布特征，以及评估其参数化穿越ACC的等密度涡动示踪剂通量的能力。这些问题将使用洛斯阿拉莫斯国家实验室（LANL）平行海洋计划（POP）的0.1度，42层全球配置来解决。在标准气候尺度海洋模式中，南大洋涡旋混合过程的表述存在很大的不确定性。涡旋的影响通常是用涡旋扩散参数化的，气候尺度模式对南大洋涡旋扩散系数的大小非常敏感。当使用恒定的涡动扩散系数而不是可变的涡动扩散系数时，海洋环流对表面强迫的敏感性是否改变仍然不清楚，更根本的是，不清楚涡动扩散模型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动扩散系数的水平和垂直分布。不同的方法导致了南大洋相互矛盾的震级和空间分布。拉格朗日浮动提供了一种方法来测试扩散模型的适用性。将在ACC内外的不同位置和不同深度的海洋模型中部署10，000个数值浮标，以估计拉格朗日扩散系数及其空间分布。这些拉格朗日扩散系数在参数化纬向综合以及当地涡示踪剂输送在ACC的技能将进行评估。该项目将有助于正在进行的努力，以调和相互矛盾的南大洋的扩散系数估计，并最终使我们能够评估扩散系数的空间结构在模拟南大洋涡通量的问题准确。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。拉格朗日方法的详细评估及其与其他方法的涡流通量和扩散率估计的关系将有利于分析部署在整个海洋的浮子的数据。特别是，在这项研究中调查的方法将有助于现场数据的解释返回的180acoustic浮子，正在部署作为NSF资助的南大洋（DIMES）实验的Diapycnal和Isopycnal混合实验的一部分。该项目是对美国CLIVAR（气候变化和可预测性）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.