Bottom Stress and the Generation of Vertical Vorticity Over the Inner Shelf

几公里大小的小漩涡在靠近海岸的浅海和深海之间的水交换中起着至关重要的作用。这些漩涡在很大程度上受海底摩擦的控制，而海底摩擦本身取决于许多参数，从海底地形的粗糙度到水柱的密度分布。最近的证据表明，简单的、可调整的底部应力公式在数值模型中比基于物理机制的更复杂的公式表现得更好。为了获得更精确的数值模型，需要更好地理解导致底部应力的小尺度物理，而不需要根据观测进行调整。这项研究将在海底附近进行详细和广泛的测量，以发展所需的认识。目前的模式描述了海底应力对近底流、由表面波和内波产生的近底速度、海底成分、河床形态以及由热、盐和悬浮沉积物引起的分层的依赖。然而，最近的区域尺度模拟表明，与基于更简单的阻力规律的模拟相比，使用这些应力模型会降低区域尺度的电流模拟。最近的测量和大涡模拟表明，Langmuir环流可能渗透到海底，破坏了近海底的流动和阻力关系，而最近的应力测量和粒子图像测速表明，长期模型可能过度预测了底部应力对表面重力波的依赖，并过度简化了大型波浪形成的沙纹上的近海底流动。这项观察性研究将把底部应力的直接协方差测量与假设影响底部阻力规律的相应量的测量相结合。它利用了一个单独资助的、同步的、位于同一地点的研究，研究内部大陆架的交换和分散，包括通过高分辨率高频雷达测量表面洋流，测量水流和分层的水柱，测量风的强迫，以及区域尺度的模拟。对结果的综合测量和模拟的分析将对底部应力动力学及其在控制千米尺度的涡流和内部大陆架运输的涡度动力学中的作用产生新的见解。智力优势：这项研究将产生一个全面的数据集，包括底部应力的测量和所有被假设影响底部阻力规律的量。对数据集的分析将产生对底部应力力学的新见解，对长期模型的评估以及尚未纳入底部应力模型的过程（如Langmuir循环）的作用，并最终改进底部应力模型的物理特性。海底应力的测量和分析将为单独资助的同步区域尺度表面速度、水柱流、分层和风强迫的测量和模拟提供重要的新元素，这将导致对内陆架垂直涡度的产生和阻尼的新认识。更广泛的影响：这项研究将改进海底应力模型，这将改进对漩涡和其他运动的预测，这些运动控制着水团和水生物质的运动，包括沉积物、幼虫和营养物质，从靠近海岸的浅滩到更大的中大陆架和外大陆架区域。改进后的预测将提高沿海科学家、工程师和规划者解决有害藻华、污染物的运输和命运以及搜索和救援行动等社会重要应用的能力。pi在WHOI和美国地质勘探局有指导的历史，并与沿海管理人员和规划者互动。该研究将支持WHOI-USGS博士后学者计划的一名近期博士毕业生，并在广泛的沿海海洋学问题、方法和应用方面提供培训和经验。

Small, kilometers-scale eddies play a critical role in the exchange of water between the shallows adjacent to the coast and the deeper ocean. These eddies are largely controlled by the friction at the sea floor, which itself depends on many parameters ranging from the roughness of the bottom topography to the density distribution in the water column. Recent evidence shows that simple, tunable formulations for bottom stress perform better in numerical models than more sophisticated ones based on physical mechanisms. Better understanding of the small-scale physics leading to bottom stress is needed for more accurate numerical models that do not need tuning with observations. This study will make detailed and extensive measurements near the sea floor to develop the needed understanding.Current models describe the dependence of the bottom stress on the near-bottom current, near-bottom velocities produced by surface and internal waves, seabed composition, bedforms, and stratification caused by heat, salt and suspended sediment. However, recent regional-scale simulations suggest that use of these stress models degrades regional-scale simulations of currents relative to those based on simpler drag laws. Recent measurements and large-eddy simulations suggest that Langmuir Circulations might penetrate to the seafloor and disrupt the near-bottom flow and drag relationships, and recent stress measurements and particle-image velocimetry suggest that the longstanding models might over-predict the dependence of the bottom stress on surface gravity waves and over-simplify the near-bottom flow over large wave-formed sand ripples. This observational study will combine direct-covariance measurements of the bottom stress with corresponding measurements of the quantities that have been hypothesized to influence the bottom drag law. It capitalizes on a separately funded, concurrent, co-located study of exchange and dispersion across the inner shelf that will include measurements of surface currents by high-resolution high-frequency radar, water-column measurements of currents and stratification, measurements of wind forcing, and regional-scale simulations. Analysis of the resulting combined measurements and simulations will produce new insights into the dynamics of the bottom stress and its role in the vorticity dynamics that govern kilometer-scale eddies and transport across the inner shelf.Intellectual Merit :This study will produce a comprehensive data set with measurements of the bottom stress and all of the quantities that have been hypothesized to influence the bottom drag law. Analysis of the data set will produce new insights into the mechanics of the bottom stress, an evaluation of longstanding models and the role of processes such as Langmuir Circulations that have not yet been incorporated into bottom stress models, and ultimately an improvement of the physics of bottom stress models. The measurements and analysis of bottom stress will contribute an important new element to the separately funded concurrent regional-scale measurements and simulations of surface velocities, water-column currents and stratification, and wind forcing, which will lead to a new understanding of the generation and damping of vertical vorticity over the inner shelf.Broader Impacts :This research will lead to improved models of the bottom stress, which will improve predictions of eddies and other motions that control the movement of water masses and water-borne substances, including sediments, larvae and nutrients, from shallows adjacent to the coast to the larger mid- and outer shelf regions. Improved predictions will enhance the ability of coastal scientists, engineers and planners to address societally important applications including harmful algal blooms, transport and fate of pollutants, and search and rescue operations. The PIs have a history of mentoring at WHOI and USGS as well as interacting with coastal managers and planners. The study will support a recent doctoral graduate in the WHOI-USGS Postdoctoral Scholar Program and provide training and experience in a wide range of coastal oceanographic problems, methods, and applications.