Internal tides in straits and small ocean basins: resonant modes vs. propagating waves

海峡和小洋盆的内潮汐：共振模式与传播波

• 批准号: 2220439
• 负责人: Varvara Zemskova
• 金额: $ 45.63万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2220439&HistoricalAwards=false
• 关键词: Internal; tides; straits; small; ocean

Tides are generated by astronomic body forces on the entire water column but in the stratified ocean, their interaction with topography or similar mechanisms also generate internal tides, which manifest themselves as a periodic displacement of the various density levels vertically from their normal resting position. These internal tides can propagate large distances away from the topography, and their dissipation away from the generation site results in ocean mixing that is thought to contribute to sustaining abyssal stratification and overturning circulation. A large number of both numerical and observational studies regarding internal tide generation have been focused on either generation at ocean ridges and isolated topographical features or generation at the open coast, but not in semi-enclosed basins, such as bays, gulfs, marginal seas, and straits. Under appropriate basin configuration, tidal forcing can elicit a resonant response for an appropriate basin geometry, yet what such “appropriate” configuration may be is yet poorly understood. Few previous works considered basin mode resonance to tidal forcing in barotropic or two-layer models. However, vertical stratification and its interaction with coastal bathymetry are likely to have a significant impact on the generation of internal waves and their dynamics within a basin. This project will conduct numerical simulations to investigate under what physical characteristics of a basin, internal tides can be characterized as resonant basin modes rather than freely-propagating waves. Satellite-based estimates of internal tide elevation (amplitude and phase) will be used to investigate in which basins resonant internal tides are observed and these estimates will be compared with numerical simulation results. Although the scope of this project is primarily focused on physical mechanisms of internal tide dynamics, the results and analysis will have broader interdisciplinary application. For instance, vertical transport due displacements of density layers by the internal tides can deliver nutrients to the surface or oxygenate the bottom waters. Such vertical mixing is important for biological productivity of a basin, especially if internal tide amplitudes, and subsequently vertical excursions, can be resonantly amplified. Analysis in this study will highlight in which basins internal tides might play an important role, especially relative to wind stress-induced mixing. Furthermore, theoretical understanding of the physical mechanisms is crucial to improving models that estimate internal tide amplitudes from satellite observations. The forthcoming launch of Surface Ocean and Water Topography (SWOT) satellite mission, which has unprecedentedly high resolution and wide spatial coverage, provides further promise for estimating internal tides. Using SWOT data in models will be particularly useful for small basins and coastal regions that are not well sampled by existing satellites. Theoretical results from this study will shed light on the new physical mechanisms for internal tide dynamics, which will be important for validating and understanding the satellite-based estimates. Additionally, this proposed project will support the professional development of an early career female oceanographerThe proposed project addresses a significant gap in literature regarding internal tides: their dynamics in small basins. Much of the previous research efforts have focused either on the interaction of internal tides with isolated bottom topography and effects on abyssal mixing in the open ocean or the generation of internal tides at coastal shelves, while there is a paucity of studies investigating the response to tidal forcing in semi-enclosed basins, such as bays, gulfs, marginal seas, and straits. However, because of their long wavelengths (comparable to horizontal basin scales), internal tides may be resonant with natural basin modes, which would explain previous observations of large amplitude internal tides in some basins. This study will build an understanding of the basin response to tidal forcing by systematically adding complexity to numerical simulations to investigate the effects of basin characteristics (e.g., size, topography, stratification) on its response. These results will shed light on the criteria for basins, where internal tide response may be amplified, thus potentially resulting in greater vertical transport and mixing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

潮汐是由整个水柱上的天体力产生的，但在分层海洋中，它们与地形或类似机制的相互作用也会产生内潮汐，其表现为各种密度水平从其正常静止位置垂直的周期性位移。潮汐可以传播到远离地形的很远的距离，并且它们远离产生地点的消散会导致海洋混合，这被认为有助于维持深海分层和大量翻转环流。关于内潮产生的数值和观测研究都集中在海脊和孤立地形特征的产生或开放海岸的产生，而不是半封闭盆地，例如海湾、海湾、边缘海和海峡。适当的盆地配置，潮汐强迫可以引发适当的盆地几何形状的共振响应，但对于这种“适当”的配置可能是什么，人们还知之甚少，以前的工作很少考虑正压潮汐强迫的盆地模式共振。然而，垂直分层及其与海岸测深的相互作用可能会对盆地内的内波及其动力学产生重大影响，该项目将进行数值模拟以研究在何种物理特征下的情况。在盆地中，内潮可以被描述为共振盆地模式，而不是基于卫星的内潮高程（幅度和相位）估计，将用于调查哪些盆地观测到共振内潮，并且将使用这些估计。与数值模拟结果相比，虽然该项目的范围主要集中在内潮汐动力学的物理机制上，但结果和分析将具有更广泛的跨学科应用，例如，内潮汐引起的密度层位移引起的垂直输送可以提供营养物质。这种垂直混合对于盆地的生物生产力非常重要，特别是如果内潮幅度和随后的垂直偏移可以共振放大，本研究中的分析将突出显示内潮可能在哪些盆地中发挥作用。一个重要的此外，对物理机制的理论理解对于改进通过卫星观测估计内潮汐振幅的模型至关重要，该卫星已发射了表面海洋和水域地形（SWOT）任务卫星。前所未有的高分辨率和广泛的空间覆盖范围，为估计内潮汐提供了进一步的希望，这对于现有卫星无法很好采样的小盆地和沿海地区特别有用。新的内部物理机制潮汐动力学，这对于验证和理解基于卫星的估计非常重要。此外，该拟议项目将支持早期职业女性海洋学家的专业发展该拟议项目解决了有关内潮汐的文献中的一个重大空白：小盆地的动态。以前的大部分研究工作都集中在内潮汐与孤立底部地形的相互作用以及对公海深海混合的影响或沿海陆架内潮汐的产生上，而很少有研究调查潮汐响应强迫然而，在半封闭盆地中，例如海湾、海湾、边缘海和海峡，由于它们的波长较长（与水平盆地尺度相比），内潮可能与自然盆地模式共振，这可以解释以前对大型盆地的观测。本研究将通过系统地增加数值模拟的复杂性来研究盆地特征（例如大小、地形、这些结果将揭示盆地的标准，其中内潮汐响应可能会被放大，从而可能导致更大的垂直运输和混合。该奖项是 NSF 的法定使命，并通过使用评估被认为值得支持。基金会的智力价值和更广泛的影响审查标准。