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。探讨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的作用至关重要。这些相互作用点之一是非洲南部的海洋地区，印度洋、南大西洋和南大洋在那里交汇。虽然现在已经确定，这一领域的海洋间交换具有全球重要性，但对决定这一交换的存在和规模的基本过程知之甚少。该项目将促进了解哪些进程负责印度洋-大西洋洋间交流，以及它们如何以及在多大程度上协同工作以实现交流。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理解，但也进一步开发了可用于许多其他海洋学问题，其他地球科学领域及其他领域的新工具。 在JEDI系统中实施并在这一高度湍流的海洋区域进行测试的完全非线性数据同化方法将是世界上独一无二的，可以由科学家和业务中心应用。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，它可以应用于纯建模研究，比较因果通路和突出模型的缺陷。学生将接触到尖端的数据同化，海洋建模和观测，以及因果发现，从而成为一个非常全面的萌芽科学家。研究结果将通过会议报告和出版物广泛传达给海洋学、气候和应用数学/工程界。许多进程已被提出对非洲南部的海洋间交换至关重要，如纳塔尔脉冲（阿古拉斯洋流的大气旋蜿蜒），莫桑比克涡旋，从马达加斯加南端脱落的偶极子，后折区的正压-斜压混合不稳定性，可能与Rossby波型海盆模态、印度尼西亚赤道气流和南赤道流的变化、热力结构的大尺度变化（包括NADW入流引起的涡度生成）、大尺度风扰动以及耦合的气候模态，例如印度洋偶极子。该项目将检验以下假设，即海洋间交换是由Agulhas回射区的紧密再循环环流控制的，而这种环流又受到上述物理过程的调节。这项研究的主要贡献将是解开和量化这些直接的贡献和非线性相互作用的贡献，使用一个新的完全非线性因果发现方法。这种方法提供了一个完整的分解这些非线性相互作用成两个过程的相互作用，三个过程的相互作用等，此外，它允许量化的贡献的大小，任何未识别的控制过程，指导研究到目前为止未知的重要物理过程。这种方法将被应用于处理时间序列从30年的再分析的海洋区域在南非周围，使用完全非线性数据同化，结合所有现有的观测，以回答以下首要的研究问题：·什么是物理过程，负责海洋间的交流？这些物理过程是如何相互作用而导致大洋间交换的？该奖项反映了NSF的法定使命，并被认为是值得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的支持。