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

将使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。其目的是解释观测到的内潮变化及其产生的非线性波。这项研究将集中在世界各地普遍存在的亚临界潮流(流速小于波速)产生的长波长线性内波(内潮)。将考察三种内部潮汐效应：变量生成、非均匀传播和向非线性波形的转换。将使用麻省理工学院的多学科模拟、估计和同化系统(MSEAS)进行一系列模拟，主要是通过与数据的比较，将静力原始方程模式调整到中尺度。模拟的配置范围从理想的水深、分层和流动条件到通过数据驱动的建模获得的现实条件。收集结果的相互比较将揭示可变的四维内部潮汐产生和传播的物理学，目的是描述这一过程是如何在真实海洋中发生的。新的MSEAS非静力模式将被用来研究非线性转换过程。通过与一个月的遥感和现场实验数据的比较，将验证结果在实际海洋中的适用性。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、表面和内潮、非线性内波的起源以及这些过程的强烈变异性的相互作用。使用不同数值方案的静力和非静力原始方程模式将被用于内潮预报。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造活动。其中包括氧气、营养物、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、以及夏季层结强烈季节的昼夜混合和水团发展模式。此外，这些海浪也是切变、强大的底层洋流以及阳光和黑暗之间的水循环的主要来源。它们是混合过程的能源，而混合过程对底栖生物栖息地、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。所有成果，包括模型产出，都将分发给海洋研究人员和社区。一名沿海海洋学学生将接受教育，一名博士后将进一步接受指导。

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.