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

在一个封闭的海洋盆地中，正压潮的行为是很容易理解的：在平面视图中，盆地模态似乎以开尔文波的形式围绕盆地的外围旋转，在北半球是逆时针的。该项目探讨了耦合斜压响应，即波长比表面潮汐小得多的盆地内部模态，是否可以对在大陆架上观测到的大内部潮汐负责。在任何地形变异性存在的情况下，正斜压模态耦合，生潮势既可以产生大振幅的盆地内部模态，也可以产生正压模态。由于斜压参数（密度异常和分层结构）随时间的变化而变化，因此斜压响应不会像正压模态那样与产潮势锁定在恒定相位。尽管如此，在比潮汐周期更长的时间内，会有一个缓慢调制的响应。对内潮的观测表明，存在沿海岸的能量通量，并且由于水平速度矢量的旋转感随深度的变化，其变量（速度、等温线位移）不符合一个简单的内波模式。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。本研究将结合理论分析、理想与现实模拟，以及以往收集资料的分析，研究沿海岸内潮的产生与传播。理论技术将用于研究沿大陆架的斜压响应在分层旋转的盆地中对盆地尺度的正压潮汐强迫。理想数值模拟将用于研究由正压开尔文波与沿陆架水深变化相互作用产生的沿海岸传播内潮的结构。正压-斜压能量转换对陆架宽度、分层、正压潮幅值和水深变异性幅值的敏感性将被量化。本文将对美国西海岸陆架和坡域进行正压潮汐产生内潮的真实模拟，以研究正斜压能量转换和沿岸内潮传播的性质。还将分析以前实地试验的长期时间序列，以确定那里的内部潮汐的空间结构和沿海岸传播的性质。知识价值。许多大陆架上的洋流变化是由内部潮汐主导的。沿岸结构和传播的性质目前尚不清楚。本研究的目的是提供一个理想的和现实的框架，以了解沿海岸内潮的捕获和传播。更广泛的影响。这项研究将支持哈特菲尔德海洋科学中心的永久展览和相关课程的发展。位于俄勒冈州纽波特的美国游客中心（HMSVC）。本研究将资助斯克里普斯海洋研究所的一名研究生，他将接受海岸物理海洋学、数值方法和实地数据分析技术方面的培训。内波和潮汐在沿海水域引起的环流是目前加利福尼亚和墨西哥太平洋沿岸关注的焦点。该项目还将使国家海洋研究所能够继续与墨西哥同事合作，设计一项关于墨西哥海岸内潮、内波和跨海岸通量的观测研究。

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.