The causal pathways of the Indian-Atlantic interocean exchange

印度-大西洋间海洋交换的因果路径

• 批准号: 2220201
• 负责人: Petrus Johannes van Leeuwen
• 金额: $ 70.82万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2220201&HistoricalAwards=false
• 关键词: causal; pathways; Indian; Atlantic; interocean

A fundamental question in physical oceanography is how different oceans interact. Answering this question is crucial for our understanding of the global ocean circulation and the role the ocean plays in the climate system. One of these interaction points is the ocean area south of Africa where the Indian, South Atlantic and Southern Oceans meet. While it is now well established that the interocean exchange in this area is of global importance, much less is known on what the underlying processes are that determine the existence and size of this exchange. This project will advance the understanding of which processes are responsible for the Indian-Atlantic inter-ocean exchange and how and to what extend they work in concert to achieve the exchange. It brings together state-of-the-art developments in nonlinear data assimilation, ocean modeling, observational data sets and nonlinear causal discovery to advance that understanding. As such the project enhances our fundamental understanding of the ocean circulation, but also further develops new tools that can be used in many other oceanographic problems, in other geoscience areas, and beyond. The fully nonlinear data assimilation method implemented in the JEDI system and tested on this highly turbulent ocean area will be unique in the world and can be applied by scientists and operational centers alike. Systematic nonlinear causal discovery is a growing and exciting research field that deserves maturing into a standard well- calibrated tool, beyond more traditional linear causal discovery methodologies. The causal discovery framework can be applied to many outstanding oceanographic and wider geoscience problems. Furthermore, it can be applied to pure modeling studies to compare causal pathways and highlight model deficiencies. A student will be exposed to cutting edge data assimilation, ocean modeling and observations, and causal discovery, leading to an exceptionally rounded budding scientist. Results of the study will be broadly communicated to the oceanographic, climate and applied mathematical/engineering communities through conference presentations and publicationsMany processes have been put forward as important for the interocean exchange S of Africa, such as Natal Pulses (large cyclonic meanders of the Agulhas Current), Mozambique Eddies, dipoles shed from the southern tip of Madagascar, mixed barotropic-baroclinic instabilities in the retroflection area, perhaps related to Rossby-wave like basin modes, variations in the Indonesian Throughflow and the South Equatorial Current, large-scale variations in the thermodynamic structure, including vorticity generation due to NADW inflow, large-scale wind perturbations, and coupled climate modes, e.g. the Indian Ocean Dipole. This project will test the hypothesis that the interocean exchange is controlled by the tight recirculation gyre in the Agulhas Retroflection area, which is in turn modulated by the physical processes mentioned. The main contribution of this research will be to unravel and quantify these direct contributions and the contributions from nonlinear interactions using a new fully nonlinear causal discovery methodology. This methodology provides for a complete decomposition of these nonlinear interactions into two-process interactions, three-process interactions etc. Furthermore, it allows to quantify the magnitude of the contributions of any unidentified controlling processes, directing research to hitherto unknown important physical processes. This methodology will be applied to process time series from a 30-year reanalysis of the ocean area around South Africa, using fully nonlinear data assimilation, incorporating all available observations to answer the following overarching research questions:• What are the physical processes that are responsible for the interocean exchange?• How do these physical processes interact to cause the interocean exchange?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

物理海洋学的一个基本问题是不同的海洋如何相互作用。回答这个问题对于我们理解全球海洋环流和海洋在气候系统中所扮演的角色至关重要。其中一个相互作用点是印度洋、南大西洋和南大洋交汇的非洲南部海域。虽然现在已经确定，这一地区的海洋间交换具有全球重要性，但人们对决定这种交换的存在和规模的基本过程知之甚少。该项目将促进对哪些过程负责印度洋-大西洋跨洋交换以及它们如何以及在多大程度上协同工作以实现交换的理解。它汇集了非线性数据同化、海洋建模、观测数据集和非线性因果发现方面的最新发展，以促进这种理解。因此，该项目增强了我们对海洋环流的基本认识，而且还进一步开发了可用于许多其他海洋学问题、其他地球科学领域以及其他领域的新工具。在JEDI系统中实施的全非线性数据同化方法，并在这一高度湍流的海洋区域进行了测试，将是世界上独一无二的，可以被科学家和作战中心应用。系统非线性因果发现是一个不断发展和令人兴奋的研究领域，值得成熟为一个标准的校准工具，超越更传统的线性因果发现方法。因果发现框架可以应用于许多突出的海洋学和更广泛的地球科学问题。此外，它可以应用于纯粹的建模研究，以比较因果途径和突出模型的不足。学生将接触到最前沿的数据同化，海洋建模和观测，以及因果发现，导致一个非常全面的崭露头角的科学家。这项研究的结果将通过会议报告和出版物广泛地传达给海洋学、气候和应用数学/工程社区。许多过程被认为对非洲南部的洋间交换很重要，如纳塔尔脉冲（阿古拉斯洋流的大旋风弯曲）、莫桑比克涡流、马达加斯加南端的偶极子漂移、反射区正斜压混合不稳定性、可能与ross - by-wave样盆地模式、印度尼西亚通流和南赤道流的变化、热力学结构的大尺度变化（包括NADW流入引起的涡度产生）、大尺度风扰动以及耦合气候模式（如印度洋偶极子）有关。该项目将测试这样一个假设，即大洋间的交换是由Agulhas反射区的紧密再循环环流控制的，而这一环流又由上述物理过程调节。本研究的主要贡献将是利用一种新的全非线性因果发现方法来揭示和量化这些直接贡献和非线性相互作用的贡献。该方法将非线性相互作用完全分解为两过程相互作用、三过程相互作用等。此外，它允许量化任何未知控制过程的贡献的大小，指导研究到目前为止未知的重要物理过程。该方法将应用于处理来自南非周围海洋区域30年再分析的时间序列，使用完全非线性数据同化，结合所有可用的观测结果来回答以下主要研究问题：•导致海洋间交换的物理过程是什么？•这些物理过程如何相互作用导致海洋间的交换？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。