The vertical propagation of internal waves through the ocean

概述：内波在海洋大范围密度分层和垂直切变结构中的垂直传播是物理海洋学中的一个重要问题。一个紧迫的问题是更好地了解从混合层底部向深海传播的内部波能流，因为这有可能影响海洋混合，从而在影响海洋环流和气候方面发挥作用。这个问题目前正被积极地研究，涉及到北冰洋由于夏季冰的消退而产生的近惯性波。然而，目前大尺度数值模式的结论与观测到的深海近惯性波能量的季节周期不一致。此外，还有其他潜在的重要场景，如由Langmuir循环激发的高频内波的能量通量和命运，以及复杂的双扩散阶梯结构的传输和反射特性，这些目前知之甚少。智力优势：本项目的智力优势在于提出并利用半解析方法来合理模拟任意分层和垂直剪切的内波传播。该方法旨在处理海洋中可能出现的具有挑战性的情况，其中分层和切变变化的垂直尺度与过境内波的垂直波长相当。理论模型将通过与实验室实验和数值模拟的比较，系统地验证日益复杂的情景。实验室实验和数值模型将使线性理论模型无法访问的非线性制度的研究成为可能。建模工作将通过一系列合作与过去、现在和未来对北太平洋和北冰洋的实地研究密切协调，使其扎根于海洋中发生的事情，首席研究员和他的研究生将参加2015年美国国家科学基金会资助的实地研究。更广泛的影响：本研究的更广泛的影响是深入了解内部波在复杂海洋分层中的传播和耗散，从而支持对影响海洋混合的机制的研究。具体来说，研究人员将提高对内部波从混合层底部通过双扩散阶梯分层向下传播和不稳定性的理解和预测能力。经过验证的理论方法将作为带有用户指南的MATLAB GUI编写并免费提供，将为解释现场数据和协助规划现场研究提供新的工具。该项目将支持麻省理工学院的一名研究生、一名本科生研究员和一名博士后的部分培训。WHOI、耶鲁大学和华盛顿大学的研究生、博士后和教师也将接受理论方法的培训。将招募一名WHOI地球物理流体动力学暑期项目的研究员参与实验，并招募MIT-WHOI联合项目的学生通过与MIT+K12项目合作，制作关于海洋的鼓舞人心的短片。理论方法和实验将被纳入环境流体动力学的研究生课程。这项研究的结果将通过期刊文章、特邀研讨会和网站传播。

Overview: The vertical propagation of internal waves through a wide range of density stratifications and vertical shear structures of the ocean is an important problem in physical oceanography. A pressing matter is to develop a better understanding of the flow of internal wave energy that propagates down towards the deep ocean from the base of the mixed layer, as this has the potential to impact ocean mixing and thus play a role in influencing ocean circulation and climate. This issue is currently being very actively pursued in regards to near-inertial waves in the Arctic Ocean due to the retreating summer ice. At present, however, the conclusions of large-scale numerical models are at odds with the observed seasonal cycle of near-inertial wave energy in the deep ocean. Furthermore, there are other potentially important scenarios such as the energy-flux and fate of high-frequency internal waves excited by Langmuir circulation, and the transmission and reflection properties of complex double-diffusive staircase structures, about which little is currently known.Intellectual Merit: The intellectual merit of this project is in the advancement and utilization of a semi-analytical method to reasonably model the propagation of internal waves through arbitrary stratifications and vertical shear. The method is designed to handle the challenging scenarios that can arise in the ocean, in which the vertical scale of variations in the stratification and shear are comparable to the vertical wavelength of the transiting internal waves. The theoretical model will be systematically validated for increasingly complex scenarios through comparison with laboratory experiments and numerical simulations. The laboratory experiments and numerical model will enable investigations of nonlinear regimes the linear theoretical model cannot access. The modeling effort will be closely coordinated with past, present and future field studies of the North Pacific and Arctic Ocean via a number of collaborations, keeping it grounded in what happens in the ocean, and both the Principal Investigator and his graduate student will participate in a 2015 NSF-funded field study.Broader Impacts: The broader impact of this research is insight into the propagation and dissipation of internal waves through complex ocean stratifications, thereby supporting investigations of mechanisms that influence ocean mixing. Specifically, the investigators will improve understanding of, and the ability to predict, the downward propagation and instability of internal waves from the base of the mixed layer and through double-diffusive staircase stratifications. The validated theoretical method, prepared as a MATLAB GUI with user guide and made freely available, will provide a new tool for interpreting field data and assisting in the planning of field studies. The project will support the training of a graduate student, an undergraduate researcher and part of the training of a postdoc at MIT. Graduate students, postdocs and faculty at WHOI, Yale and University of Washington will also be trained in the theoretical method. A fellow of the WHOI Geophysical Fluid Dynamics summer program will be recruited to participate in experiments, and MIT-WHOI Joint Program students will be recruited to produce short and inspiring educational videos on the ocean through collaboration with the MIT+K12 program. The theoretical method and experiments will be incorporated in a graduate course on environmental fluid dynamics. The results of this study will be disseminated through journal articles, invited seminars and a website.