Tidal Mixing Fronts: Stability and Cross-frontal Transport in the Presence of Tides, Topography and Bottom Stress

潮汐混合锋：潮汐、地形和底部应力存在下的稳定性和跨锋面传输

• 批准号: 1059632
• 负责人: Kenneth Brink
• 金额: $ 55.29万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-01 至 2014-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1059632&HistoricalAwards=false
• 关键词: Tidal; Mixing; Fronts; Stability; Cross

Tidal mixing fronts form at the boundary between stratified waters and waters that are homogenized by tidal turbulence. The mechanism for their development thus requires that bottom friction and tidal advection are important at lowest order. In addition, a sloping bottom (since tidal amplitude varies with water depth) will generally be present. These fronts have been studied using ocean observations, simulation models, simplified linear stability models and in the laboratory. There does not appear to be any study in the literature that combines a broad, realistic parameter space with a simple, process orientation to investigate the linear and nonlinear stability of tidal mixing fronts.This project will study tidal mixing frontal stability systematically. The approach will be to use a hierarchy of models, starting with a numerical continuously stratified linear stability model (that can include a sloping bottom and bottom friction). The next step will be to treat a comparable finite-amplitude stability problem using a primitive equation numerical model. At this stage, cross-frontal eddy fluxes of heat and nutrients will be quantified and parameterized, building on existing approaches. The third stage uses a more realistic model, forced by tides, that is initialized with uniform stratification, and then develops a tidal mixing front (and so requires a realistic turbulence closure model). This frontal model will be used to treat finite-amplitude stability in the presence of realistically large dissipation and tidal advection. Again, the instability rates will be quantified, along with cross-frontal eddy fluxes. This forced model may, depending on tidal forcing and surface heating, reach a statistically steady frontal configuration.Finally, this third level of model will be used (in two- and three-dimensional forms) to evaluate four potentially important mechanisms of cross-frontal transport (eddy transport, mean cross- frontal flow, tidal shear dispersion and wind driving). It is very likely that nutrient and heat transport behave differently, and so they will be evaluated separately.Intellectual Merit: The intellectual merit of this project lies in its systematic treatment of tidal mixing frontal stability and consequent eddy-driven transports. The stability models will, for the first time outside of a simulation model, deal with the importance of bottom stresses, turbulent mixing and oscillating tidal advection. The fluxes will be quantified and parameterized, and will be compared with modeled fluxes associated with other potential effects, including winds. Knowing which transport mechanisms are important in a given context will help us make better use of observations and of simulation models.Broader impact: This research will shed light on the processes that drive the high biological productivity associated with tidally mixed areas, such as Georges Bank. As such, it should be useful both to biological oceanographers, and, potentially, for improved ocean prediction. In addition, the project will support a graduate student to pursue the more realistic physical and biological ramifications of this project.

潮汐混合锋形成于分层水域和被潮汐湍流均匀化的水域之间的边界。因此，它们的发展机制要求底部摩擦和潮汐平流在最低阶是重要的。此外，通常会出现一个倾斜的底部（因为潮汐振幅随水深而变化）。利用海洋观测、模拟模式、简化线性稳定性模式和实验室对这些锋面进行了研究。文献中似乎没有任何研究将广阔的、现实的参数空间与简单的过程取向结合起来研究潮汐混合锋的线性和非线性稳定性。本项目将系统研究潮汐混合锋稳定性。该方法将使用层次模型，从数值连续分层线性稳定性模型（可以包括倾斜底部和底部摩擦）开始。下一步将使用原始方程数值模型来处理类似的有限振幅稳定性问题。在这一阶段，将在现有方法的基础上对热量和营养物质的横锋涡旋通量进行量化和参数化。第三阶段使用更现实的模型，受潮汐的强迫，初始化为均匀分层，然后发展为潮汐混合锋（因此需要一个现实的湍流闭合模型）。该锋面模型将用于处理实际存在的大耗散和平流的有限振幅稳定性。再一次，不稳定率将被量化，连同交叉锋涡通量。这种强迫模式，取决于潮汐强迫和地表加热，可能达到统计上稳定的锋面形态。最后，将使用第三层模式（以二维和三维形式）来评估四种可能重要的锋交叉输送机制（涡旋输送、平均锋交叉流动、潮汐切变弥散和风驱动）。很可能养分和热量的传输行为不同，因此将分别对它们进行评估。知识价值：本项目的知识价值在于系统地处理了潮汐混合、锋面稳定性和随之而来的涡流驱动运输。稳定性模型将首次在模拟模型之外处理底部应力、湍流混合和振荡潮汐平流的重要性。通量将被量化和参数化，并将与与其他潜在影响（包括风）相关的模拟通量进行比较。了解在给定环境中哪些传输机制是重要的，将有助于我们更好地利用观测和模拟模型。更广泛的影响：这项研究将阐明驱动与潮汐混合地区相关的高生物生产力的过程，如乔治滩。因此，它不仅对生物海洋学家有用，而且可能对改进海洋预测有用。此外，该项目将支持研究生追求这个项目更现实的物理和生物后果。