The Antarctic Circumpolar Current: a Fractured Transport Barrier

近年来，剩余平均理论在南大洋的应用，极大地提高了我们对涡旋输送如何控制南大洋南极绕极流（ACC）的层化和涡旋翻转的理解。然而，这一模式牢牢植根于一个二维或区域一体化的框架，这与最近南大洋研究的一个主要主题背道而驰：最近的研究结果表明，涡动-平均流相互作用，这是负责产生和维持特征的非均匀锋面结构的ACC，沿着ACC路径变化显著，不同区域之间的过渡主要受地形控制。因此，越来越多的证据表明，南大洋的区域平均模型不足以解决对运输和倾覆率的控制。该项目的目标是双重的。第一个是定量和动态地描述南大洋涡动热和位涡通量的区域变化。特别感兴趣的是过渡的ACC前的垂直结构和它们的有效性附近的地形运输障碍。在这个项目中，假设，即南大洋的纬向输送发生在由流动与地形的相互作用所决定的离散位置，将进行测试。这种离散的ACC视图的一个主要分支是潜在的敏感性，全球传输特性的本地强迫变化。第二个目标是提供一个更好的动力学描述的流动地形相互作用进行一套过程研究模型。从涡流通量分布中获得的洞察力将用于开发和测试预测这些“运输走廊”空间范围的缩放参数。“这项研究还将考虑这种局部行为如何对强迫条件的变化作出反应。智力优势：遥感技术和计算能力的进步意味着，在过去十年中，对南大洋进行建模和观测的能力有了很大进步。从模型和观测中获得的见解强调了ACC. Yet内的水文结构和动力学行为的异质性，目前的理解，控制这种区域变化的机制仍然不发达。由于南大洋是全球环流系统中水团交换和水团改变的主要场所，因此记录ACC中运输和混合过程的空间分布对于了解其在气候系统中的作用至关重要。该项目试图超越南大洋翻转的纬向平均观点，其目标是使我们对ACC的基本动力学理解与观测数据和海洋全球气候模型相一致。由于这一区域通常是海洋环流模型中约束最差的方面，因此从系统的过程研究建模方法中获得的见解将有助于指导涡旋海洋环流模型的改进和对此类模型结果的解释，这些模型可能对垂直分辨率和地形特征的表示敏感。该项目将为一名博士后研究员提供培训，他将有机会在加州理工学院和夏威夷大学两个令人振奋的环境中工作。与日本JAMSTEC的同事在分析其高分辨率海洋模型结果期间进行的国际合作也是该项目的一个重要方面。

In recent years, the application of residual mean theory to the Southern Ocean has greatly improved our understanding of how eddy transport controls the stratification and meridional overturning of the Southern Ocean's Antarctic Circumpolar Current (ACC). Yet, this model is firmly rooted in a two-dimensional, or zonally-integrated, framework, which runs counter to a major theme of recent Southern Ocean research: the large degree of zonal asymmetry in dynamical properties of the ACC. Recent results have shown that eddy-mean flow interactions, which are responsible for generating and sustaining the characteristic heterogeneous frontal structure of the ACC, vary significantly along the path of the ACC with transitions between different regions largely controlled by topography. Thus there is increasing evidence that zonally-averaged models of the Southern Ocean are insufficient to resolve controls on transport and overturning rates. The goals of this project are two-fold. The first is to quantify and dynamically describe the regional variability of eddy heat and potential vorticity fluxes in the Southern Ocean. Of particular interest are transitions in the vertical structure of the ACC fronts and their effectiveness as transport barriers near topography. In this project, the hypothesis, that meridional transport in the Southern Ocean occurs in discrete locations determined by flow interactions with topography will be tested. A major ramification of this discrete view of the ACC is the potential sensitivity of global transport properties to local forcing changes. The second goal is to provide a better dynamical description of flow-topography interactions by conducting a suite of process study models. Insight gained from the eddy flux distributions will be used to develop and test scaling arguments that predict the spatial extent of these "transport corridors." This study will also consider how this localized behavior responds to changes in forcing conditions. Intellectual Merit: Advances in remote sensing techniques and in computational power have meant that the ability to model and observe the Southern Ocean has progressed significantly over the past decade. Insight gained from both models and observations have emphasized the heterogeneity of the hydrographic structure and dynamical behavior within the ACC. Yet, the current understanding of the mechanisms that control this regional variability remains underdeveloped. As the Southern Ocean is the primary site of water mass exchange and water mass modification in the global circulation system, documenting the spatial distribution of transport and mixing processes in the ACC is essential for understanding its role in the climate system. This project attempts to move beyond the zonally-averaged view of Southern Ocean overturning with the goal of bringing our fundamental dynamical understanding of the ACC in line with both observational data and ocean global climate models.Broader Impacts: This project will contribute to our understanding of Southern Ocean circulation. As this region is typically the most poorly constrained aspect of ocean general circulation models, insight gained from a systematic process-study modeling approach will help to guide improvements in eddying ocean circulation models and interpretation of results from such models, which may be sensitive to vertical resolution and representation of topographic features. The project will provide training to a post-doctoral researcher who will have the opportunity to work in two stimulating environments at Caltech and the University of Hawaii. The international collaboration with colleagues at JAMSTEC in Japan during analysis of their high-resolution ocean model results is also an important aspect of the project.