The vertical propagation of internal waves through the ocean

概述：内波通过海洋的各种密度层和垂直剪切结构的垂直传播是物理海洋学中的一个重要问题。当务之急是更好地了解从混合层底部向下传播到深海的内波能量流动，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。由于夏季冰川消退，北冰洋的近惯性波目前正在非常积极地处理这一问题。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季节周期并不一致。此外，还有其他潜在的重要场景，如由朗缪尔环流激发的高频内波的能量通量和去向，以及复杂的双扩散楼梯结构的传输和反射特性，目前对此知之甚少。智力价值：该项目的智力价值在于提出和利用了一种半解析方法，以合理地模拟内波通过任意分层和垂直剪切的传播。该方法旨在处理海洋中可能出现的具有挑战性的情况，在这种情况下，层结和切变的垂直变化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，对日益复杂的场景进行系统验证。实验室实验和数值模型将使线性理论模型无法进入的非线性区域的研究成为可能。建模工作将通过一系列合作与北太平洋和北冰洋过去、现在和未来的实地研究密切协调，使其立足于海洋中发生的事情，首席研究员和他的研究生都将参加2015年由NSF资助的实地研究。广泛影响：这项研究的更广泛影响是洞察复杂海洋层结中内波的传播和消散，从而支持对影响海洋混合的机制的调查。具体地说，研究人员将提高对内波从混合层底部和通过双扩散阶梯层结向下传播和不稳定的理解和预测能力。经过验证的理论方法将提供一种新的工具，用于解释野外数据和协助实地研究的规划。该项目将支持对一名研究生、一名本科生研究员的培训，以及麻省理工学院博士后培训的一部分。世界卫生组织、耶鲁大学和华盛顿大学的研究生、博士后和教职员工也将接受理论方法培训。WHOI地球物理流体动力学暑期项目的一名研究员将被招募参加实验，麻省理工学院-WHOI联合项目的学生将被招募通过与麻省理工学院K12项目的合作制作关于海洋的简短且鼓舞人心的教育视频。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、特邀研讨会和一个网站传播。

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.