The Zonal Overturning Circulation

海洋中的垂直输送是耦合气候系统的一个重要组成部分，因为它们能够将热量、碳、营养物质和其他示踪剂带入或移出表面混合层，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经向翻转环流上，这是一种二维纬度/深度投影。实际上，翻转环流是三维的，在垂直和斜流输送中有很大的纬向变化，通常在不同的纬度，由纬向流连接起来。这个项目将研究纬向翻转环流，二维经向翻转的三维非纬向平均方面。主要的焦点将放在沿中纬度西部边界的预期上升流上，这将反映过去已经检查过的沿东部边界的下升流，两者都与沿岸压力梯度有关。在几个模式中发现这种上升流具有显著的输送强度，影响中上层水柱，并可能影响这些水对大气的暴露、海气交换、热盐储存和变率。该项目将利用高分辨率理想数值模型、低分辨率和高分辨率现实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。这项工作将深入了解西部边界上升流在全球气候系统中的作用，为研究生提供支持，为研究生和本科生课程内容做出贡献，包括WHOI GFD暑期学校和特拉华大学的课程，并通过WHOI暑期学生研究员计划和特拉华大学的本科生参与其中。活的程序。计划通过网页和美国Del。一年一度的海岸日演讲。提出的研究的主要目标是：应用理想模式和边界层理论的层次结构，以获得维持中纬度西部边界观测到的压力梯度的基本理解，以及这与三维海洋环流和热输送的关系；在现实的低分辨率和高分辨率海洋状态估计中诊断垂直输送和浮力预算，并将这些发现与理想的建模和理论联系起来；利用拉格朗日诊断法诊断西界附近上升流的源区及其上升流后的命运，包括可能夹带入地表混合层和对海气相互作用的影响。理想的建模将基于HYCOM原语方程模型，该模型可以配置为纯等轴、z坐标、sigma坐标或这些坐标系的组合。该模型将应用于越来越复杂的配置，以便更好地隔离和理解控制纬向翻转环流源水的物理特性。现实模拟将包括来自“海洋环流和气候估算（ECCO）”联盟的两个海洋状态估计：低分辨率、非涡分辨的ECCO第4版（ECCO v4）；以及允许涡流的ECCO，第二阶段（ECCO2）。除了研究控制上升流的动力学外，该模型还将用于探索上升流的来源和命运，在一定的初始深度范围内引入示踪剂和浮子。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。

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.