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存在横跨盆地的近地表向东流动，这种流动通常表现为一组不同的洋流和急流。这些电流已经在观测中探测到，并在数值模式中进行了模拟。与此同时，他们的潜在动力仍不明朗。在这一点上，它们的流向与埃克曼和斯维尔德鲁普理论预测的西向相反。此外，它们似乎与澳大利亚西海岸的勒温流(Lc)和更大规模的环流，即印度尼西亚贯流(ITF)和南大洋有关。因此，向东流动代表了我们对SiO中大尺度平均流动的理解上的一个根本差距。该项目将使用对现场观测和数值模型的分析来填补这一空白。观测分析将依赖于三个主要数据集。每个数据集都将ARGO数据与历史数据结合起来，不同的测绘技术产生的产品具有适合分析不同方面的特点：CSIRO开发的CARS数据集是一个高质量的月平均数据集，它包含T、S和其他水团属性，它能够追踪水团；IPRC数据集并入了额外的绝对动态地形产品，能够估计绝对地转速度；而UTAS数据集绘制了ARGO和历史数据在密度面上的图，这将有助于解决更精细的锋面特征和描绘下降流/上升区的特征。卫星风将被用来计算Ekman和Sverdrup流，并迫使模型。为了测试关于控制表面东向流的过程的具体假设，将使用海洋环流模型。研究小组结合了IPRC、CSIRO和塔斯马尼亚大学的科学家的才华，后者的科学家将他们在SIO现场观测的广泛知识贡献给该项目更广泛的影响：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。此外，这些洋流与LC和ITF相互作用，很可能是由于LC内部和南极绕极洋流附近的下沉涌流而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在SiO年代际变化中起重要作用。这一结果可能也适用于其他海洋中的类似特征。

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.