Dynamics of near-surface eastward flows in the South Indian Ocean

目标和知识价值：热带和亚热带南印度洋（SIO）上层海洋环流的一个显著方面是近地表东流穿过盆地的存在，它经常表现为一组不同的流和喷流。这些电流已在观测中被探测到，并在数值模式中得到模拟。与此同时，它们的潜在动力仍不明朗。在这方面，它们与Ekman和Sverdrup理论预测的向西流动方向相反。此外，它们似乎与沿澳大利亚西海岸的Leeuwin洋流（LC）和更大规模的环流，即印度尼西亚通流（ITF）和南大洋有关。因此，东向流代表了我们对SIO大尺度平均流的理解的一个基本空白。本项目将利用现场观测分析和数值模型来填补这一空白。观测分析将依赖于三个主要数据集。每个数据集都将Argo数据与历史数据相结合，不同的制图技术产生的产品具有适合不同分析方面的特征：CSIRO开发的CARS数据集是一个高质量的T、S和其他水质量属性的月平均数据集，可以追踪水团；IPRC数据集结合了绝对动态地形的附加产品，允许估计绝对地转速度；UTas数据集将Argo和历史数据映射到密度表面上，这将有助于解决更精细的锋面特征和表征下行/上升流区域。卫星风将用于计算埃克曼流和斯维德鲁普流，并加强模型。为了检验控制表面向东流的过程的具体假设，将使用一个海洋环流模型。该研究团队结合了IPRC、CSIRO和塔斯马尼亚大学的科学家的才能，以及后者机构的科学家为“更广泛的影响：了解这些一阶特征的动力学对于验证和改进气候模型是必要的”项目贡献了他们在SIO现场观测的广泛知识。此外，这些流与大陆架和ITF相互作用，并且可能是大陆架内部和南极环极流附近的下流关闭的盆地尺度翻转环流的一部分。因此，地面东向流的动力应该在SIO年代际变化中发挥重要作用。研究结果可能适用于其他海洋的类似特征。

Objectives and intellectual Merit: A remarkable aspect of the upper-ocean circulation in the tropical and subtropical South Indian Ocean (SIO) is the presence of near-surface, eastward flow across the basin, which often appears as a set of distinct currents and jets. These currents have been detected in observations and simulated in numerical models. At the same time, their underlying dynamics remain unclear. In this regard, they flow counter to the westward direction predicted by both Ekman and Sverdrup theory. Furthermore, they appear to be linked to the Leeuwin Current (LC) along the west coast of Australia and to larger-scale circulations , namely, the Indonesian Throughflow (ITF) and the Southern Ocean. Thus, the eastward flow represents a fundamental gap in our understanding of the large-scale mean flow in the SIO. This project will use analyses of in situ observations and numerical models to fill that gap. The observational analysis will rely on three main datasets. Each dataset combines Argo data with historical data, the different mapping techniques resulting in products with characteristics suited to different aspects of the analysis: the CARS dataset developed at CSIRO is a high-quality monthly-mean dataset of T , S , and other water-mass properties, which allows for tracing watermasses; the IPRC dataset incorporates the additional product of absolute dynamic topography, allowing an estimation of absolute geostrophic velocity; and the UTas dataset maps Argo and historical data on density surfaces, which will be useful in resolving finer frontal features and characterizing downwelling/upwelling regions. Satellite winds will be used to compute Ekman and Sverdrup flows and to force the models. To test specific hypotheses about the processes that control the surface eastward currents, an ocean circulation model will be used.The research team combines the talents of scientists at the IPRC, CSIRO, and the University of Tasmania, with scientists at the latter institutions contributing their extensive knowledge of in situ observations in the SIO to the project Broader Impact: Understanding the dynamics of these first-order features is necessary to validate and improve climate models. Moreover, these currents interact with the LC and the ITF, and are likely part of a basin-scale overturning circulation closed by downwelling within the LC and near the Antarctic Circumpolar Current. The dynamics of the surface eastward currents therefore should play an important role in SIO decadal variability. The results will likely apply to similar features in the other oceans.