Collaborative Research: Diagnosing Eddy mixing in DIMES

气候尺度的海洋模型一致强调海洋颠覆环流在十年和更长时间尺度上对地球气候和生物地球化学循环所起的关键调节作用。然而，在寻求解决许多地区性气候问题的过程中，这些模型的可信度受到了挑战，因为它们对南大洋混合过程的表现极为敏感。模型行为的这种特殊性反映了混合在调解南极绕极流(ACC)水团垂直和水平输送中的独特作用，这些水团通过各自对倾覆率和洋际交换的影响来塑造倾覆环流。南大洋浮游和浮游混合实验收集了大量数据来量化混合，包括一种化学示踪剂的扩散和150个浮标在两个不同深度的扩散。这项建议的目的是分析示踪剂和浮动数据，以估计横向涡旋混合中的垂直和水平变化。主要研究人员以前的工作表明，示踪剂和漂浮物本身不足以准确限制这些变化。因此，这些数据将与替代示踪剂和平流浮子一起进行分析，并对研究中的区域进行数值模拟。智力上的好处：这个项目解决了量化小尺度涡旋在大范围环流中的作用这一艰巨的问题。由于这些漩涡的观测和建模具有很大的挑战性，因此很难量化它们的大规模影响。事实上，在气候模型中，下个世纪海洋对热量和碳的吸收在参数化中尺度涡旋的模型中可能与明确解决这些问题的模型截然不同。这意味着，目前的参数化要么忽略了中尺度涡旋混合的水平和垂直变化，要么不能正确地表示中尺度涡旋混合的垂直变化，可能没有能力做出准确的气候预测。该项目的目标是在数据中建立对涡旋混合的新理解，并利用这些结果为气候模型开发新的参数。数据和模型之间的联系是确保DIMES实验将在气候界留下长期遗产的关键。广泛影响：该项目解决了通过海洋中的涡流及其在气候系统中的作用来量化混合的重要问题。此外，这项工作应放在研究湍流中的涡流-平均流相互作用的更广泛的背景下进行。这些想法对大气和行星大气的一般循环具有重要意义，特别是对像木星这样的气体巨星的大气。事实上，在参数上，海洋与木星非常相似，其涡旋尺度比大尺度环流的涡旋尺度小数百倍。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/世界卫生组织联合项目的学生介绍南大洋在气候系统中的作用，这是一个强有力的教育组成部分。DIMES项目是由美国CLIVAR(气候可变性和可预测性)项目赞助的过程研究。

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.