Collaborative Research: Causes and Effects of Shelf-Edge Internal Tide Variability

将采用四维数值模拟和诊断方法研究大陆斜坡附近的内部潮汐产生和传播。目的是解释观测到的内潮变化及其产生的非线性波浪。该研究将集中研究在世界各地普遍存在的亚临界潮汐流（流速小于波速）产生的长波线性内波（内潮）。三种内部潮汐效应将被检查：变量产生，异质传播和转换到非线性波形。一组模拟将使用麻省理工学院多学科模拟、估计和同化系统（MSEAS）进行，主要是通过与数据比较，在中尺度上调整了流体静力学原始方程模型。建模的配置范围将从理想的水深、分层和流动条件到通过数据驱动建模获得的现实条件。将收集到的结果进行相互比较将揭示可变四维内部潮汐产生和传播的物理特性，目的是描述这一过程在真实海洋中是如何发生的。新的MSEAS非流体静力模型将用于研究非线性转换过程。研究结果是否适用于实际海洋，将通过与遥感和为期一个月的实地实验数据进行比较来核实。这项工作将有助于更好地理解和准确模拟中尺度和亚中尺度特征、表面和内部潮汐、非线性内波的起源以及这些过程的强变异性的相互作用。使用不同数值格式的静力和非静力原始方程模型将被评估用于内部潮汐预测。内潮和非线性内波及其与更大尺度的相互作用影响着广泛的自然和人为活动。其中包括氧气、营养物质、浮游生物、鱼类和其他捕食者的生命周期和分布，海军行动和监视，水下声学，以及强烈分层的夏季水流混合和水团发展的模式。此外，这些波浪是切变的主要来源，强大的海底流，以及日光和黑暗之间的水循环。它们是混合过程的能量来源，对底栖生物栖息地、浮游生物和鱼类的生命周期以及营养物质和污染物的分布都很重要。所有结果，包括模式产出，将分发给海洋研究人员和社区。对一名沿海海洋学学生进行培训，对一名博士后进行进一步指导。

Internal tide generation and propagation near continental slopes will be studied using a four-dimensional numerical simulation and diagnosis approach. The purpose is to explain observed variability in internal tides and the nonlinear waves they spawn. The study will concentrate on long wavelength linear internal waves (internal tides) generated from sub-critical tidal flow (current speed less than wave speed), ubiquitous around the world. Three internal tide effects will be examined: variable generation, heterogeneous propagation, and conversion to nonlinear waveform. A set of simulations will be performed with the MIT Multidisciplinary Simulation, Estimation, and Assimilation System (MSEAS), mostly with the hydrostatic primitive equation model already tuned at mesoscales via comparison with data. Modeled configurations will range from idealized bathymetric, stratification, and flow conditions to realistic conditions obtained via data-driven modeling. Inter-comparisons of the collected results will divulge the physics of variable four-dimensional internal tide generation and propagation, with the intent of describing how the process occurs in the real ocean. The new MSEAS non-hydrostatic model will then be used to study nonlinear conversion processes. Applicability of the results to the real ocean will be verified via comparison to remote sensing and in situ data from a one-month long experiment.This work will lead to better understanding and accurate modeling of interactions of mesoscale and sub-mesoscale features, surface and internal tides, origins of nonlinear internal waves, and strong variability of these processes. Hydrostatic and non-hydrostatic primitive equation models using different numerical schemes will be evaluated for internal tide predictions. Internal tides and nonlinear internal waves, and their interactions with larger scales, impact a wide range of natural and man-made activities. These include life cycles and distributions of oxygen, nutrients, plankton, fish, and other predators, naval operations and surveillance, underwater acoustics, and patterns of diapycnal mixing and water mass development in the summer season of strong stratification. In addition, these waves are a major source of shear, strong bottom currents, and cycling of water between sunlight and darkness. They are energy sources for mixing processes which are important to benthic habitat, plankton and fish life cycles, and distributions of nutrients and contaminants. All results, including model outputs, will be disseminated to ocean researchers and communities. A coastal oceanography student will be educated and a post-doctoral fellow further instructed.