Subpolar-Subtropical Connectivity of the North Atlantic Circulation

海洋凭借其巨大的储热能力，在地球气候和气候变化中起着至关重要的作用。自1955年以来，全球海洋的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显示，自20世纪90年代初以来，北大西洋（包括亚极地地区）迅速变暖、变咸。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多年代际变率模式从寒冷阶段向温暖阶段的转变。这些年代际气候转变涉及北大西洋副热带和亚极地环流的横向变化，以及大西洋经向翻转环流（AMOC）的垂直变化，AMOC是全球热量和淡水环流系统的关键组成部分。北大西洋环流的研究集中在纽芬兰大浅滩周围的过渡区，在那里边界流和喷流、再环流和中尺度涡旋（长度尺度通常小于100公里）的影响占主导地位。强烈的相互作用发生在这个过渡区，横向在亚极环流和副热带环流之间，垂直在大西洋经向环流（AMOC）的冷暖分支之间。有证据表明，这个相对紧凑的区域在更大范围内改变甚至调节AMOC方面起着关键作用，因此对大西洋的长期年代际变化很重要。然而，尽管有许多观测项目，这个地区的动态和影响还没有得到很好的理解。该项目将通过研究亚极环流和副热带环流的连通性，有助于了解太平洋环流的变异性。这种模式-数据综合的结果将对耦合气候模型具有特别重要的意义，这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为教育工作者提供的各种在线资源/互动工具、为高中生提供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有关海洋气候研究的科学素养。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。通过在亚极地和亚热带北大西洋进行的主要观测项目，海洋学家在更好地了解这些子盆地内AMOC的结构和变化方面取得了重大进展。本文提出的工作通过关注与控制两者之间环流有关的关键问题以及亚极和亚热带连通性在多大程度上调节了更大规模的AMOC，从而补充了这些观察结果。本项目旨在阐明控制过渡区环流的物理动力学，特别是涡旋和西深边界流的相对重要性，并记录过渡区在更大尺度环流中的作用和影响，特别是北大西洋亚极和亚热带AMOC和水性质在年际到年代际和更长的时间尺度上的变化。涡旋和时间平均环流的相互作用是全球气候变率预测面临的最大挑战之一，本项目可采用细网格分辨率模式对其进行研究。这些目标将通过执行详细的模型数据综合研究来实现，结合使用混合坐标海洋模型（HYCOM）和现有观测（卫星测高、漂浮物、水文、示踪剂和系泊阵列）的一套高分辨率大西洋模拟的数值结果。通过对水团输送和转化、被动示踪剂、位势涡度和动量通量的分析，对三维大西洋环流进行量化。结果表明，旋解HYCOM代表了过渡区和大尺度北大西洋的基本环流特征，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.