The Zonal Overturning Circulation

海洋中的垂直输送是耦合气候系统的重要组成部分，因为它们能够将热量、碳、营养物质和其他示踪剂移入和移出表面混合层，在那里它们可以与大气交换。几乎所有关于海洋翻转环流的研究都集中在二维子午线翻转环流，这是一种二维纬度/深度投影。事实上，翻转的环流是三维的，垂直和昼夜输送的纬向变化很大，通常在不同的纬度，它们由纬向气流连接在一起。这个项目将研究这个纬向翻转环流，即二维子午线翻转的三维非纬向平均方面。主要焦点将是沿中纬度西部边界预计的上升流，预计将反映过去研究过的沿东部边界的下降流，两者都与近岸压力梯度有关。这种上升流在几个模型中被发现，具有显著的输送强度，影响到中上层水柱，并可能影响这些水域对大气的暴露、海气交换、热和盐的储存和变化性。该项目将利用高分辨率理想化数值模式、低分辨率和高分辨率实际状态估计以及边界层理论，将上升流区域的大小、水平和垂直尺度与其基本驱动机制、地面风应力和浮力强迫联系起来。这项工作将提供对西部边界上升在全球气候系统中的作用的洞察，支持一名研究生，为研究生和本科课程内容做出贡献，包括WHOI GFD暑期班和特拉华大学的课程，并让本科生参与WHOI暑期学生伙伴计划和U Del。REU程序。公众宣传计划通过网页和《每日邮报》进行。拟议研究的主要目标是：应用一系列理想化模式和边界层理论，从根本上了解是什么维持了中纬度西部边界沿线观测到的气压梯度，以及这与三维海洋环流和热量输送之间的联系；在实际的低分辨率和高分辨率海况估计中诊断垂直输送和浮力预算，并将这些结果与理想化的模拟和理论相联系；利用拉格朗日诊断来诊断西部边界附近上涌的水域的来源区及其在上涌后的去向，包括可能卷入表层混合层和对海-气相互作用的影响。理想化建模将基于HYCOM原始方程模型，该模型可以配置为纯等轴、z坐标、西格玛坐标或这些坐标系的组合。该模型将应用于日益复杂的构型，以便更好地隔离和理解控制纬向翻转环流源水的物理机制。实际模拟将包括“估计海洋环流和气候(ECCO)”联盟的两个海洋状态估计：低分辨率、非涡流分辨率ECCO版本4(ECCO V4)和允许涡流的ECCO，第二阶段(ECCO2)。除了研究控制上升流的动力学，这些模型还将用于探索上升流的来源和命运，使用示踪剂和浮标在一定的初始深度范围内引入。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Vertical transports in the ocean are an important component of the coupled climate system because they are able to move heat, carbon, nutrients, and other tracers into and out of the surface mixed layer, where they can be exchanged with the atmosphere. Almost all research on the Ocean’s overturning circulation has focused on the two-dimensional Meridional Overturning Circulation, a two-dimensional latitude/depth projection. In reality the overturning circulation is three-dimensional, with large zonal variations in vertical and diapycnal transports, often at different latitudes, that are connected by zonal flows. This project would examine this Zonal Overturning Circulation, the three-dimensional non-zonally averaged aspects of the two-dimensional Meridional Overturning. The primary focus will be on the expected upwelling along midlatitude western boundaries, which is expected to mirror the downwelling along eastern boundaries that has been examined in the past, both associated with alongshore pressure gradients. This upwelling is found in several models at significant transport magnitudes, affecting the middle to upper water column and potentially influencing the exposure of those waters to the atmosphere, air-sea exchange, heat and salt storage and variability. The project will relate the magnitude, horizontal, and vertical scales of the upwelling regions to their fundamental driving mechanisms, surface wind stress, and buoyancy forcing, using high resolution idealized numerical models, low and high resolution realistic state estimates, and boundary layer theory. The work will provide insight into the role of western boundary upwelling in the global climate system, support a graduate student, contribute to graduate and undergraduate course content, including the WHOI GFD summer school and classes at U. Delaware, and involve undergraduates through the WHOI summer student fellow program and the U. Del. REU program. Public outreach is planned through webpages and the U. Del. annual Coast Day presentations.The primary objectives of the proposed study are: to apply a hierarchy of idealized models and boundary layer theory to gain a fundamental understanding of what maintains the observed pressure gradient along mid-latitude western boundaries and how this connects to the three-dimensional ocean circulation and heat transport; to diagnose vertical transports and buoyancy budgets in realistic low- and high-resolution ocean state estimates and relate these findings to the idealized modeling and theory; and to use Lagrangian diagnostics to diagnose the source regions of waters upwelled near the western boundary and their fate after upwelling, including possible entrainment into the surface mixed layer and influence on air-sea interaction. Idealized modeling will be based on the HYCOM primitive equation model, which can be configured as purely isopycnal, z-coordinate, sigma-coordinate, or a combination of these coordinate systems. The model will be applied in increasingly complex configurations in order to better isolate and understand the physics controlling the source waters for the zonal overturning circulation. Realistic modeling will include two ocean state estimates from the “Estimating the Circulation and Climate of the Ocean (ECCO)” consortium: the low-resolution, non-eddy resolving ECCO version 4 (ECCO v4); and the eddy-permitting ECCO, phase II (ECCO2). In addition to examining the dynamics controlling upwelling, the models will also be used to explore the source and fate of upwelled water, using the introduction of both tracers and floats at a range of initial depths.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.