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

潮汐混合锋形成于分层沃茨和被潮汐湍流均匀化的沃茨之间的边界处。因此，它们的发展机制要求底摩擦和潮汐平流在最低阶是重要的。此外，通常会出现倾斜的底部（因为潮汐幅度随水深而变化）。利用海洋观测、模拟模型、简化的线性稳定性模型和在实验室中对这些锋面进行了研究。在文献中，似乎没有任何研究结合了广泛的，现实的参数空间与简单的，过程的方向来研究潮汐混合锋的线性和非线性稳定性，本项目将系统地研究潮汐混合锋的稳定性。该方法将使用一系列模型，从数值连续分层线性稳定性模型（可包括倾斜底部和底部摩擦）开始。下一步将是处理一个可比的有限振幅稳定性问题，使用原始方程数值模型。在这一阶段，将在现有方法的基础上对热量和营养物质的跨锋面涡流通量进行量化和参数化。第三阶段使用一个更真实的模型，由潮汐推动，初始化为均匀分层，然后开发一个潮汐混合锋（因此需要一个真实的湍流闭合模型）。该锋面模型将用于处理实际大耗散和潮汐平流存在下的有限振幅稳定性。同样，不稳定率将被量化，沿着与横锋涡通量。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跨锋输送机制（涡流输送、平均跨锋流、潮汐切变弥散和风驱动）。这是很有可能的，营养和热量传输的行为不同，所以他们将分别评估。智力优点：这个项目的智力优点在于它的潮汐混合锋面稳定性和随之而来的涡驱动传输系统的治疗。稳定性模型将首次在模拟模型之外处理海底应力、湍流混合和振荡潮汐平流的重要性。这些通量将被量化和参数化，并将与包括风在内的其他潜在影响相关的模拟通量进行比较。了解在特定情况下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：这项研究将揭示驱动与潮汐混合区相关的高生物生产力的过程，如乔治银行。因此，它应该对生物海洋学家有用，并有可能改善海洋预测。此外，该项目将支持研究生追求更现实的物理和生物的影响，这个项目。

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.