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文体力产生的，但是在分层的海洋中，它们与地形或类似机制的相互作用也会产生内部潮汐，这表现为从正常静止位置垂直垂直的各种密度水平的周期性位移。这些内部潮汐可以使远离地形的大距离传播，它们的耗散远离生成地点会导致海洋混合，这被认为有助于维持深渊分层和推翻循环。有关内部潮汐产生的数值和观察性研究都集中在洋山脊上的一代和孤立的地形特征或开放式海岸的孤立的地形特征或一代，但在半封闭的贝斯（例如海湾，海湾，边际海洋和strais）中却没有。在适当的盆地配置下，潮汐强迫可以引起适当的盆地几何形状的谐振反应，但是这种“适当”的配置可能尚不清楚。以前很少有作品认为盆地模式共振在正压或两层模型中的潮汐强迫。但是，垂直分层及其与沿海测深的相互作用可能会对内部波的产生及其动力学产生重大影响。该项目将进行数值模拟，以研究盆地的物理特征，内部潮汐可以将其表征为谐振盆地模式，而不是自由传播波。基于卫星的内部潮汐升高（振幅和相）的估计值将用于研究哪些基础知识共振的内部潮汐，并将这些估计值与数值模拟结果进行比较。尽管该项目的范围主要集中在内部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，由于内部潮汐的密度层的垂直转运可以将养分传递到表面或氧合水域。这种垂直混合对于盆地的生物生产力很重要，尤其是如果内部潮汐放大器以及随后的垂直偏移可以得到共鸣。在这项研究中的分析将突出显示低音内部潮汐可能起重要作用，尤其是相对于风应力引起的混合。此外，对物理机制的理论理解对于改善估计内部潮汐放大器的模型至关重要。即将推出地面海洋和水地形（SWOT）卫星任务，该任务是前所未有的高分辨率和广泛的空间覆盖范围，为估计内部潮汐提供了进一步的希望。在模型中使用SWOT数据将特别有用，对于现有卫星并未很好地采样的小鲈鱼和沿海地区。这项研究的理论结果将阐明内部潮汐动力学的新物理机制，这对于验证和理解基于卫星的估计值很重要。此外，这个拟议的项目将支持一名早期职业女性海洋学家的专业发展，拟议的项目提出了有关内部潮汐的显着差距：他们的小鲈鱼动态。以前的许多研究工作都集中在内部潮汐与孤立的底部地形之间的相互作用以及对公海中深渊混合的影响，或者在沿海货架上产生内部潮汐的产生，而研究很少研究研究对潮汐强迫的反应，例如半粘着的贝斯，例如bays，bays，bays，bays，bays，gulfs，gulfs，marginal serais and Strais和Strais和Strais和Strais和Strais。但是，由于其长波长（与水平盆地尺度相当），内部潮汐可能与天然盆地模式共振，这可以解释某些低音中大型放大器内部潮汐的先前观察结果。这项研究将通过系统地将复杂性添加到数值模拟中，以研究盆地特征（例如，大小，地形，分层）对其响应的影响，从而对盆地对潮汐强迫的反应建立理解。这些结果将阐明贝斯的标准，其中可能会放大内部潮汐反应，从而可能导致更大的垂直运输和混合。该奖项反映了NSF的法定任务，并通过使用基金会的知识分子优点和更广泛的影响标准来评估NSF的法定任务。