NSF/GEO-NERC: Stirring at the Walls - A Dynamical Boundary Model for the Ocean

许多海洋环流变化发生在日到月的时间尺度和几十到几百公里的长度尺度上，这一范围被称为“中尺度”。这些特征可以反馈更大尺度的海洋环流（高达“盆地尺度”- 6000公里），并且对于确定年际到年代际时间尺度上的海洋环流非常重要。然而，在模型中，中尺度特征需要比流域尺度特征更精细的网格来表示它们，因此，气候模拟所需的长时间全球范围内的直接数值分辨率远远超出了当前的计算机资源。该项目将使用“动态边界模型”（DBM）代替模型边界的高分辨率网格。该项目将首先开发一个DBM，可将其纳入现有的现实全球气候模型。然后通过与边界附近高分辨率模型的比较来评估性能。最后，该项目将使用现实模型和DBM实现来研究边界混合。总体合作将支持一名博士后、一名研究生和一名来自代表性不足人群的本科生。这项工作具有广泛的社会意义，因为成功将代表着全球气候数值模拟和预测的重大技术进步。基本的方法是将海洋划分为相互作用的独立区域：一个包含一般海洋环流的外部区域和一个具有不同动力学的狭窄边界层，称为DBM。在数学上，这是通过引入一个测量薄边界层厚度与海洋盆地大水平尺度之比的小参数来实现的。在较小尺度上，边界层方程变成非线性波动方程，允许海岸波浪破裂，能量耗散，流体在边界混合，并反馈到内部动力学中。为了将这项工作扩展到非理想几何，边界层方程将被推广到包括海岸曲率和跨海岸深度剖面，垂直壁上的开尔文波将被海岸困波取代。一旦建立了一种可靠、快速的边界/内部相互作用方法，DBM将直接插入到全球气候原始方程（PE）模式中。使用密集嵌套网格的PE模型来明确解析边界层的并排数值实验将与使用DBM在较粗分辨率下运行的实验进行比较。本项目由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与本国有关的调查人员提供资金。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。

Much of ocean circulation variability occurs over time scales of days to months and length scales of 10s to 100s of km, a range known as the 'mesoscale'. These features can feedback on the larger scales of circulation in the ocean (up to 'basin scale' - 6000 km), and are important in determining ocean circulation on interannual to decadal timescales. Yet mesoscale features require much finer grids to represent them in models than basin scale features, so their direct numerical resolution over the entire globe for the long times required in climate simulations is far beyond current computer resources. This project will use a 'Dynamical Boundary Model' (DBM) instead of high resolution grids at model boundaries. This project will first develop a DBM that can be incorporated into existing realistic global climate models. Then performance will be evaluated by comparison to models with high resolution near boundaries. Finally, the project will investigate mixing at boundaries using realistic models with the DBM implementation. The overall collaboration will support a post-doctoral fellow, a graduate student, and an undergraduate from an under-represented demographic. The work has broad social relevance, as success would represent a significant technical step forward in numerical modeling and prediction of global climate. The basic methodology is to split the ocean into separate interacting regions: an outer region that encompasses the general ocean circulation and a narrow boundary layer with different dynamics, referred to as a DBM. Mathematically, this is accomplished by the introduction of a small parameter that measures the ratio of the thin boundary layer thickness to the large horizontal scale of the ocean basin. At smaller scales, the boundary layer equation becomes a nonlinear wave equation allowing coastal waves to break, energy to be dissipated and fluid to mix at the boundary, and feeds back into the interior dynamics. To extend this work to non-idealized geometry, the equations for the boundary layer will be generalized to include coastal curvature and cross-shore depth profiles, and Kelvin waves on vertical walls will be replaced by coastal trapped waves. Once a reliable and rapid method has been derived for the boundary/interior interaction, the DBM will be inserted directly into global climate primitive equation (PE) models. Side-by-side numerical experiments using PE models with dense nested grids to explicitly resolve the boundary layer will be compared with those run at coarser resolution using the DBM. This project is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with their own country.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.