Subpolar-Subtropical Connectivity of the North Atlantic Circulation

海洋通过其巨大的储热能力，在地球气候和气候变化中发挥着关键作用。自1955年以来，全球海洋变暖约占地球系统变暖的93%。然而，这种变暖既不是空间上均匀的，也不是时间上恒定的。叠加在全球长期趋势上的是年际到年代际时间尺度和区域到流域尺度的气候变率。卫星高度计和水文观测表明，自1990年代初以来，北大西洋，包括次极地区域，迅速变得更加温暖和咸。一种新的情况是，北大西洋最近20年左右的变暖在一定程度上代表了大西洋数十年变化模式从寒冷阶段向温暖阶段的过渡。这些十年气候转变涉及北大西洋亚热带和亚极地环流的横向变化和大西洋经向翻转环流（AMOC）的垂直变化，AMOC是全球热量和淡水循环系统的关键组成部分。北大西洋环流的这项研究集中在纽芬兰大浅滩周围的过渡区，边界流和射流，再循环和中尺度涡旋（长度尺度通常小于100公里）的影响占主导地位。强相互作用发生在这个过渡区，横向之间的副极地和副热带环流和垂直之间的冷，暖支的大西洋经向环流（AMOC）。有证据表明，这个相对紧凑的区域在更大的尺度上改变甚至调节AMOC方面发挥着关键作用，因此对大西洋的长期十年变化非常重要。然而，尽管有许多观测领域的计划，该地区的动态和影响还没有得到很好的理解。该项目将通过解决副极地和副热带环流的连通性，帮助了解AMOC的可变性。这种模式数据综合的结果对于耦合气候模式将具有特别重要的意义，而耦合气候模式对于理解和预测全球气候变化至关重要。该项目的教育/推广部分将侧重于通过各种在线资源/教育工作者互动工具、面向高中生的佛罗里达州立大学青年学者计划和“学校科学家”计划，在K-12学校、大学和当地社区培养海洋气候研究方面的科学素养。最后，申请的资金将支持一名初级教员和一名研究生，他们将接受海洋建模、数据分析和解释方面的培训。通过正在进行的亚极地和亚热带北大西洋的主要观测项目，海洋学家们正在朝着更好地了解这些次流域内AMOC的结构和变化方面取得重大进展。这里提出的工作补充了这些意见，重点是关于什么控制之间的流通和多少次极地到亚热带连接调制较大规模的AMOC的关键问题。该项目旨在阐明控制过渡区环流的物理动力学，特别是涡旋和深西部边界流的相对重要性，并记录过渡区对大尺度环流的作用和影响，特别是亚极地和亚热带北大西洋从年际到年代际和更长时间尺度的AMOC和水性质的变化。涡旋和时间平均环流的相互作用是预测全球气候变率的最大挑战之一，可以用本项目中的细网格分辨率模式进行研究。这些目标将通过进行详细的模型数据综合研究来实现，该研究将利用混合坐标海洋模型（HYCOM）和现有观测（卫星测高、漂流物/浮标、水文学、示踪剂和系泊阵列）进行的一套高分辨率大西洋模拟的数值结果结合起来。三维大西洋环流将进行量化的水质量传输和转换，被动示踪剂，位涡和动量通量的分析。结果表明，涡分辨HYCOM代表了过渡区和大尺度北大西洋环流的基本特征，包括时间平均结构和时间变率。

The ocean, through its large capacity to store heat, plays a critical role in Earth's climate and climate variability. Warming of the world's oceans since 1955 accounts for approximately 93% of the warming of the Earth system. However, this warming is neither spatially uniform nor temporally constant. Superimposed on the global long-term trend is climate variability on inter-annual to inter-decadal time scales and regional to basin scales. Satellite altimeters and hydrographic observations show that the North Atlantic, including the sub-polar region, has rapidly become warmer and saltier since the early 1990s. An emerging picture is that the most recent 20 years or so of warming in the North Atlantic represents, in part, a transition of the Atlantic multi-decadal variability pattern from a cold to a warm phase. These decadal climate transitions involve changes both laterally in the sub-tropical and sub-polar gyres of the North Atlantic and vertically in the Atlantic Meridional Overturning Circulation (AMOC), a key component of the global heat and freshwater circulation system. This study of the North Atlantic circulation concentrates on a transition region around the Grand Banks of Newfoundland, where the effects of boundary currents and jets, recirculations, and mesoscale eddies (length scales typically less than 100 km) are dominant. Strong interactions occur in this transition region, laterally between the subpolar and subtropical gyres and vertically between the cold and warm limbs of the Atlantic Meridional Circulation (AMOC). There is evidence that this relatively compact region plays a key role in altering and even modulating the AMOC over a much larger scale and thus is important for the long-term, decadal variability of the Atlantic Ocean. Yet, despite many observational field programs, the dynamics and impacts of this region are not well understood. The project will contribute to understanding the variability of the AMOC by addressing the connectivity of the sub-polar and the sub-tropical gyres. The results of this model-data synthesis will be of particular significance to coupled climate models, which are central to understanding and predicting global climate change. The educational/outreach components of this project will be focused on cultivating scientific literacy with regards to ocean climate research in K-12 schools, at the university level, and in the local community through a variety of online resources/interactive tools for educators, the Florida State University Young Scholars program for high school students, and the "Scientists in the Schools" program. Finally, the requested funding will support a junior faculty member and a graduate student who will be trained in ocean modeling, data analysis and interpretation.Through ongoing major observation programs in the sub-polar and sub-tropical North Atlantic Ocean, oceanographers are making great strides toward a better understanding of the structure and variability of the AMOC within these sub-basins. The work proposed here complements these observations by focusing on key questions pertaining to what controls the circulation in between and how much the sub-polar to sub-tropical connectivity modulates the larger scale AMOC. This project aims to elucidate the physical dynamics that controls circulation in the transition region, especially the relative importance of the eddies and the deep western boundary current, and document the role and impact of the transition region on the larger scale circulation, especially the variability of the AMOC and water properties in the sub-polar and sub-tropical North Atlantic from inter-annual to decadal and longer time scales. The interaction of eddies and time mean circulations represents one of the greatest challenges to prediction of global climate variability, and it can be studied with the fine-grid resolution model included in this project. These objectives will be met by performing a detailed model-data synthesis study, combining numerical results from a suite of high-resolution Atlantic simulations using the HYbrid Coordinate Ocean Model (HYCOM) and existing observations (satellite altimetry, drifters/floats, hydrography, tracers, and mooring arrays). The three-dimensional Atlantic circulation will be quantified by performing analysis of water mass transport and transformation, passive tracers, and potential vorticity and momentum fluxes. It has been demonstrated that the eddy-resolving HYCOM represents the basic circulation features in the transition region and larger scale North Atlantic Ocean, including both time mean structure and temporal variability.