Tidal-Band and High-Frequency Internal Waves on the Inner Shelf

本研究将通过三种分析方法，利用历史数据、有针对性的高频内大陆架观测和实际数值模型输出，来表征和理解俄勒冈州内大陆架内波的变化。历史数据来自沿海海洋跨学科研究伙伴关系收集的俄勒冈州中部内陆架10多年的观测记录，以及西北网络海洋观测系统协会自2007年以来维护的中陆架系泊。数据包括系泊水柱速度和水的性质（温度、盐度）。内部大陆架数据集还包括高频采样原位系泊和Argus视频遥感的组合，以捕获oror Yaquina Head周围的高频非线性内波场。将对2010年和2011年夏季进行的实验数据进行分析，以确定大陆架内部的高频内部运动与近海大陆架过程（如内部潮汐、浮力羽流、上升流锋）之间的关系。由于系泊观测记录在空间上必然是有限的，因此将结合观测数据分析具有实际水深和强迫条件的流体静力学三维数值模型（ROMS）的输出，以研究内部潮汐在俄勒冈内陆架的传播和到达。内大陆架是沿海分层海洋的最后一段，可能是内波的终点。本研究将探讨不同的海洋背景条件和外部强迫是如何引起内波在大陆架上传播时的时空变化的。这包括可变风、分层、潮下流、潮汐强迫和表面波条件的影响。它还将提供这些背景条件如何改变内部波能和潜在质量向内大陆架输送的估计。由于内部潮汐在时间上是间歇性的，因此将使用复杂解调或小波分析将内部潮汐分量从速度和温度数据中分离出来。将采用时间序列技术（例如滞后相关、经验正交函数）来探索大陆架内部潮汐能量如何与近海过程、外部强迫和背景海洋条件有关的若干假设。智力优势：内波是连接近岸环境和近海大陆架环流的重要环节。利用广泛的历史数据记录，将描述简单和复杂地形区域的大范围背景海洋和强迫条件下的潮带内波变率。这项工作将揭示这些机制的年际变化，并开始解决这些过程如何随时间变化的问题。了解这些过程也将有助于了解大陆架上能量耗散和混合区域的位置。最后，Argus技术的使用将解决岸基视频遥感监测内部大陆架高频内波的实用问题。更广泛的影响：了解大陆架内部潮汐是海洋生态学和生物地球化学的兴趣所在。例如，潮间带无脊椎动物的招募与内部潮汐事件有关。此外，研究区域靠近亚奎纳河的入口，这是一个小型沿海河口的例子，那里有活跃的牡蛎养殖和商业渔业。了解决定这些河口源水含量的过程对于有效的河口管理至关重要，特别是因为大陆架水已被发现呈酸性且溶解氧含量低。在沿海数值模型中，内波通常是未解决的，与建模者合作将允许本研究和建模社区之间的反馈。最后，本项目主要支持研究生的论文研究和科学训练。

This study will characterize and understand the variability of internal waves on the Oregon inner shelf through three analysis approaches using historical data, targeted high-frequency inner-shelf observations and realistic numerical model output. The historical data come from a 10+ year observational record of the central Oregon inner shelf collected by the Partnership for Interdisciplinary Studies of Coastal Oceans, and a mid-shelf mooring maintained by the Northwest Association of Networked Ocean Observing Systems since 2007. Data include moored water-column velocity and water properties (temperature, salinity). The inner-shelf data set also includes a combination of high-frequency sampling in-situ moorings and Argus video remote sensing to capture the high-frequency nonlinear internal wave field around Yaquina Head, OR. Data from experiments conducted in summer 2010 and 2011 will be analyzed to establish the relationship between high-frequency internal motions on the inner shelf and offshore continental shelf processes (e.g. internal tides, buoyant plumes, upwelling fronts). Since moored observational records are necessarily limited in space, output from a hydrostatic, 3-dimensional numerical model (ROMS) with realistic bathymetry and forcing conditions will be analyzed in conjunction with the observational data to study the propagation and arrival of internal tides to the Oregon inner shelf.The inner shelf is the last stretch of stratified coastal ocean and is potentially the termination point for internal waves. This study will investigate how various oceanic background conditions and external forcing induce temporal and spatial variability in internal wave evolution as they propagate across the shelf. This includes the effects of variable wind, stratification, subtidal currents, tidal forcing, and surface wave conditions. It will also provide estimates of how internal wave energy and potential mass transport to the inner shelf are modified by these background conditions. Because the internal tide is intermittent in time, complex demodulation or wavelet analysis will be used to isolate the internal tidal component from velocity and temperature data. Time series techniques (e.g., lagged correlations, empirical orthogonal functions) will be employed to explore a number of hypotheses of how inner-shelf internal tide energy relates to offshore processes, external forcing and background oceanic conditions.Intellectual Merit: Internal waves are an important link connecting nearshore environments to offshore shelf circulation. With the extensive historical data record, tidal-band internal wave variability will be described for a wide range of background oceanic and forcing conditions over regions of both simple and complex topography. This work will uncover interannual variability in these mechanisms and begin to address the question of how these processes might change over time. Understanding these processes will also provide insight into locating regions of energy dissipation and mixing on the continental shelf. Lastly, the use of Argus technology will address the utility of shore-based video remote sensing to monitor high-frequency internal waves across the inner shelf.Broader Impact: Understanding inner-shelf internal tides is of interest in marine ecology and biogeochemistry. For example, recruitment of intertidal invertebrates has been linked to internal tide events. Furthermore, the study region is near the entrance to the Yaquina river - an example of a small coastal estuary with active oyster farming and commercial fishing industries. Understanding the processes that determine the source water content to these estuaries is crucial for effective estuarine management especially as shelf waters have been found to be acidic and low in dissolved oxygen. Internal waves are often unresolved in coastal numerical models and collaborating with modelers will allow for a feedback between this research and the modeling community. Finally, this project primarily supports the dissertation research and scientific training of a graduate student.