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

小的、大尺度的漩涡在邻近海岸的浅水区和更深的海洋之间的水交换中起着关键作用。这些涡流在很大程度上受海底摩擦力的控制，而海底摩擦力本身又取决于从海底地形粗糙度到水柱密度分布等许多参数。最近的证据表明，简单的，可调配方的底部应力表现更好的数值模型比更复杂的物理机制的基础上。更好地了解小尺度物理导致底部应力是需要更准确的数值模型，不需要调整与观察。这项研究将在海底附近进行详细和广泛的测量，以取得必要的了解，海流模型说明海底应力对近底海流、表面波和内波产生的近底速度、海底组成、床形以及热、盐和悬浮沉积物造成的分层的依赖关系。然而，最近的区域规模的模拟表明，使用这些应力模型降低区域规模的模拟电流相对于那些基于简单的阻力定律。最近的测量和大涡模拟表明，朗缪尔环流可能会渗透到海底，破坏近底流动和阻力的关系，最近的应力测量和粒子图像测速表明，长期存在的模型可能会过度预测海底应力对表面重力波的依赖性，并过度简化了近底流动的大型波浪形成的沙纹。这项观测研究将把海底应力的联合收割机直接协方差测量与影响海底阻力定律的假设量的相应测量结合起来。它利用了一项单独供资、同时进行、在同一地点进行的关于整个内大陆架的交换和扩散的研究，其中将包括用高分辨率高频雷达测量表层海流、水柱测量海流和分层、测量风力和区域规模的模拟。分析所产生的综合测量和模拟将产生新的见解的动态的底部应力和它的作用，在涡度动态，管理更大规模的漩涡和运输的内部shelf.Intellectual优点：这项研究将产生一个全面的数据集与测量的底部应力和所有的量，已被假设影响的底部阻力法。对数据集的分析将产生对海底应力力学的新见解，对长期存在的模型和尚未纳入海底应力模型的朗缪尔循环等过程的作用进行评价，并最终改进海底应力模型的物理学。海底应力的测量和分析将为单独供资的同时进行的区域尺度表面速度、水柱流和分层以及风力的测量和模拟提供一个重要的新要素，这将导致对内大陆架垂直涡度的产生和衰减有新的认识。这项研究将导致底部应力的改进模型，这将改善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，从靠近海岸的浅滩到较大的中陆架和外陆架区域。改进的预测将提高沿海科学家、工程师和规划人员的能力，以处理具有社会重要性的应用，包括有害藻华、污染物的迁移和归宿以及搜索和救援行动。PI有在WHOI和USGS指导以及与沿海管理者和规划者互动的历史。该研究将支持WHOI-USGS博士后奖学金计划的一名博士毕业生，并提供广泛的沿海海洋学问题，方法和应用方面的培训和经验。

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.