Collaborative Research: Diagnosing Eddy mixing in DIMES

气候尺度海洋模式一致强调海洋翻转环流在十年和更长时间尺度上对地球气候和地球化学循环的关键调节作用。然而，在寻求解决许多局部气候问题的过程中，这些模式的可信度受到了挑战，因为它们对南大洋混合过程的代表性极其敏感。模型行为的这种特性反映了混合在调节南极绕极流（ACC）中水团的垂直和水平输送方面的独特作用，这些水团通过各自对翻转率和海洋间交换的影响形成翻转环流。“南大洋纵贯和等密度混合实验”收集了大量数据，以量化混合情况，包括化学示踪剂和两个不同深度150个浮标的扩散情况。本建议的目的是分析示踪剂和浮子数据，以估计横向涡流混合的垂直和水平变化。主要研究人员以前的工作表明，示踪剂和浮子本身不足以精确地限制这些变化。因此，数据将与替代示踪剂和漂浮物一起进行分析，并对所研究的区域进行数值模拟。智力优点：本项目解决了量化大尺度环流中小尺度涡旋作用的艰巨问题。由于这些漩涡很难观察和建模，因此很难量化它们的大规模影响。事实上，在气候模式中，下一个世纪海洋吸收热量和碳的情况，在参数化中尺度涡旋的模式中与明确解决它们的模式相比可能非常不同。这意味着，目前的参数化，忽略或不正确地代表中尺度涡动混合的水平和垂直变化，可能没有技能，使准确的气候预测。该项目的目标是对数据中的涡旋混合有新的理解，并利用这些结果为气候模式开发新的参数化。数据和模型之间的联系是确保DIMES实验在气候界具有长期影响的关键。更广泛的影响：该项目解决了量化海洋涡旋混合及其在气候系统中的作用的重要问题。此外，应在湍流中涡流-平均流相互作用研究的更广泛背景下看待这项工作。这些想法对大气层和行星大气层的一般循环具有重要意义，特别是像木星这样的气体巨星。事实上，从参数上讲，海洋与木星非常相似，其涡流规模比大尺度环流小数百倍。最后，通过培训三名研究生和两名博士后，以及开发新的课程，向麻省理工学院/世界卫生组织联合计划的学生介绍南大洋在气候系统中的作用，有一个强大的教育组成部分。DIMES项目是由美国CLIVAR（气候变化和可预测性）计划赞助的过程研究。

Climate-scale ocean models unanimously stress the key regulatory function played by the oceanic overturning circulation in the Earth's climate and biogeochemical cycles over decadal and longer time scales. Yet in their quest to resolve many topical climate problems, the models' credibility is challenged by their extreme sensitivity to the representation of mixing processes in the Southern Ocean. This peculiarity of model behavior reflects the unique role of mixing in mediating the vertical and horizontal transports of water masses in the Antarctic Circumpolar Current (ACC), which shape the overturning circulation through their respective impacts on the overturning rate and inter-ocean exchange. The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) has collected a wealth of data to quantify mixing, including the spreading of a chemical tracer and of 150 floats at two different depths. The goal of this proposal is to analyze the tracer and float data to estimate the vertical and horizontal variations in lateral eddy mixing. The principal investigators' previous work has shown that tracer and floats are, by themselves, insufficient to accurately constrain these variations. Therefore the data will be analyzed together with surrogate tracers and floats advected with a numerical simulation of the regions under study.Intellectual Merit: This project tackles the formidable problem of quantifying the role of small-scale eddies in the large-scale circulation. Because these eddies are so challenging to observe and model, it is difficult to quantify their large-scale effect. Indeed the ocean uptake of heat and carbon over the next century in climate models can be very different in models that parameterize mesoscale eddies compared to models that explicitly resolve them. This implies that present parameterizations, which either ignore or improperly represent the horizontal and vertical variations in mesoscale eddy mixing, may not have the skill to make accurate climate projections. The goal of this project is to ground new understanding of eddy mixing in data and use these results to develop new parameterizations for climate models. The connection between data and models is key to ensure that the DIMES experiment will have a long term legacy in the climate community.Broader Impacts: This project addresses the important problem of quantifying mixing by eddies in the ocean and their role in the climate system. Furthermore the work should be seen in the wider context of studies of eddy-mean flow interaction in turbulent flows. The ideas have importance for the general circulation of the atmosphere and of planetary atmospheres, particularly those of the gas giants such as Jupiter. Indeed, parametrically, the ocean is closely akin to Jupiter, with an eddy scale that is hundreds of times smaller than that of the large-scale circulation. Finally, there is a strong educational component through the training of three graduate students and two post-docs, and the development of new curricula to introduce students in the MIT/WHOI Joint Program to the role of the Southern Ocean in the climate system.The DIMES project is a process study sponsored by the U.S. CLIVAR (climate variability and predictability) program.