Collaborative Research: Along-coast structure and propagation of internal tides

正压潮汐在封闭洋盆中的行为是很好理解的：在平面图中，盆地模似在北半球逆时针方向上以开尔文波的形式围绕盆地的外围旋转。该项目探索耦合斜压反应，即波长比表面潮汐小得多的内部盆地模式，是否可以对在大陆架上观察到的大内潮负责。在任何地形变率的情况下，正压和斜压模式是耦合的，而且生潮潜力可以产生大幅度的内盆模式和正压模式。由于斜压参数(密度异常和层结结构)随时间变化，斜压响应不会像正压模式那样与引潮潜势锁定在恒定的位相中。尽管如此，在比潮汐周期更长的时间里，将会有一个缓慢调制的反应。对内潮的观测表明，存在沿海岸的能量流，而且这些变量(速度、等温线位移)并不符合简单的单模内波，因为水平速度矢量的旋转感随深度而变化。然而，这种行为与浅滩深度上的斜压摩擦开尔文波是一致的。这项研究将结合理论分析、理想化和现实的模拟以及对先前收集的数据的分析，来研究沿海岸传播的内潮的产生和传播。理论技术将被用来研究在层状旋转盆地中沿大陆架对盆地尺度正压潮汐强迫的斜压响应。理想化的数值模拟将被用来研究正压开尔文波与陆架水深变化相互作用所产生的沿海岸传播的内潮的结构。正压能量转换对陆架宽度、层结、正压潮汐幅度和水深变化幅度的敏感性将被量化。美国西海岸陆架和斜坡区将进行正压潮汐内部潮汐产生的真实模拟，以研究正压到斜压能量转换和沿海内潮传播的本质。还将分析以前现场试验的长期时间序列，以确定那里的内潮空间结构和沿海岸传播的性质。许多大陆架上的海流变化是由内潮主导的。沿海岸结构和传播的性质目前尚不清楚。这项研究旨在提供一个理想化和现实化的框架，用来理解沿海诱捕和内部潮汐的传播。这项研究将支持在位于俄勒冈州纽波特的哈特菲尔德海洋科学中心-S游客中心(HMSVC)开发永久展览和相关课程。斯克里普斯海洋研究所的一名研究生将得到这项研究的支持，并将接受沿海物理海洋学、数值方法和现场数据分析技术方面的培训。由内波和潮汐引起的近海环流目前是加利福尼亚州和墨西哥太平洋沿岸的关注焦点。该项目还将使私人投资机构能够继续与墨西哥同事合作，设计一项关于墨西哥海岸外的内潮、内波和跨岸通量的观测研究。

The behavior of the barotropic tide in a closed ocean basin is well understood: in plan view the basin modes appear to rotate around the periphery of the basin as Kelvin waves, in the counter- clockwise sense in the northern hemisphere. This project explores whether the coupled baroclinic response, internal basin modes of much smaller wavelength than the surface tide, can be responsible for the large internal tides that are observed on the continental shelf. In the presence of any topographic variability, the barotropic and baroclinic modes are coupled, and the tide generating potential can generate large amplitude internal basin modes as well as barotropic modes. Because the baroclinic parameters (density anomaly and stratification structure) vary in time, the baroclinic response is not expected to be locked in constant phase with the tide generating potential, as is the barotropic mode. Nonetheless there will be a response that is slowly modulated, over times that are longer than a tidal period. Observations of internal tides reveal that there exists an along-coast energy flux, and that the variables (velocities, isotherm displacements) do not conform to a simple mode one internal wave, because the sense of rotation of the horizontal velocity vector changes with depth. That behavior is however consistent with baroclinic frictional Kelvin waves over shoaling depth.This study will combine theoretical analyses, idealized and realistic simulations and analyses of previously collected data to study the generation and propagation of along-coast propagating internal tides. Theoretical techniques will be used to investigate baroclinic response along continental shelves to basin-scale barotropic tidal forcing in a stratified, rotating basin. Idealized numerical simulations will be used investigate the structure of along-coast propagating internal tides generated by barotropic Kelvin waves interacting with along-shelf bathymetric variations. The sensitivity of barotropic to baroclinic energy conversion to shelf width, stratification, amplitude of barotropic tide and amplitude of bathymetric variability will be quantified.Realistic simulations of internal tide generation by barotropic tides will be conducted for U.S. west coast shelf and slope domains to investigate barotropic to baroclinic energy conversion and the nature of along-coast internal tide propagation. Long-term time series from previous field experiments also will be analyzed to determine the spatial structure of internal tides there and the nature of along-coast propagation.Intellectual Merit. Current variability on many continental shelves is dominated by internal tides. The nature of along-coast structure and propagation is currently not known. This study aims to provide the idealized and realistic framework with which to understand along-coast trapping and propagation of internal tides.Broader Impacts. This study will support the development of a permanent exhibit and related curriculum at the Hatfield Marine Science Center?s Visitor Center (HMSVC) in Newport, OR. A graduate student at Scripps Institution of Oceanography will be supported by this study and will be trained in coastal physical oceanography, numerical methods, and in field data analysis techniques. The circulation induced in coastal waters by internal waves and tides are currently the focus of attention along the Pacific coast of California and Mexico. This project will also allow the PIs to continue their collaboration with Mexican colleagues in the design of an observational study of internal tides, internal waves and cross-shore fluxes off the Mexican coast.