Scattering of Baroclinic Kelvin Waves by Sills in Straits

本项目将运用解析与数值模拟的方法，研究海峡浅海浅海对海岸开尔文波的冲击。它的动机是过去二十年来在印度尼西亚通流（ITF）通道进行的测量项目。在赤道印度洋产生的开尔文波已经被证明偶尔穿透这些通道，经常一次逆转ITF的分支长达一个月。最近的测量揭示了这些逆转的垂直结构，以及与通过开尔文波有关的海峡内垂直相位传播的证据。目前的推测将海峡内观测到的垂直传播与入射波的垂直传播联系起来，但该项目将证明情况可能涉及相当复杂的问题。这项工作将为理解ITF通道中的观测提供一个动力学基础。建立了一个初步的分析模型，结果令人满意。单一斜压模态的入射波将在通道内和经过通道的盆地内散射成垂直传播。海峡将改变入射垂直传播脉冲的频率内容，导致传输和旁路脉冲的垂直传播特性与入射脉冲的垂直传播特性不同。该项目将开发初步分析模型，为基本假设、误差估计和有效性限制提供理由。然后对模型预测进行分析，以获得对各种影响最直观的物理理解。数值过程模式将用于了解更真实的耗散、边界条件和底部地形对模式预测的影响。最后，将使用一个区域数值模式来尝试再现ITF段落中的观测结果，并根据更理想化的模式所揭示的潜在动力学来解释这些观测结果。智力优势：本研究阐明了海峡和渠道的基底对斜压结构和入射海岸开尔文波垂直传播的影响，将推动地球物理流体动力学理论的发展。更广泛的影响：印度尼西亚通流是全球海洋翻转环流上层分支的重要环节，而海洋翻转环流又是地球气候系统的重要组成部分。众所周知，印度洋开尔文波会间歇性地影响ITF，以至于频繁地改变气流方向，但这些影响的复杂垂直和时间结构现在才开始被理解，而且它们在全球模式中参数化得很差。虽然这项研究的目的不是改进全球气候模式的参数化，但它的贡献至少将提高对为了成功地模拟全球系统而必须参数化的内容的认识。该项目将为一名研究生提供支持，并训练该学生掌握必要的分析和数值模拟技术，以便在海洋动力学方面做出进一步贡献。

This project will utilize analytical and numerical modeling to study how shallow sills in channels and straits impact incident coastal Kelvin waves. It is motivated by measurement programs over the past two decades in the passages carrying the Indonesian Throughflow (ITF). Kelvin waves generated in the equatorial Indian Ocean have been shown to penetrate these passages episodically, often reversing branches of the ITF for up to a month at a time. Recent measurements have revealed a vertical structure to these reversals and evidence of vertical phase propagation within the straits associated with passing Kelvin waves. Speculation at present connects the vertical propagation observed within the straits to vertical propagation of the incident waves, but the project will demonstrate that the situation can involve considerable complexity. The work will provide a dynamical foundation for understanding the observations in the ITF passages. A preliminary analytical model has been developed which shows promising results. An incident wave of a single baroclinic mode will be scattered into vertical propagation in the channel and in the basin past the channel. A strait will alter the frequency content of an incident vertically propagating pulse, resulting in vertical propagation characteristics of the transmitted and bypassed pulses that are different from those of the incident pulse. The project will develop the preliminary analytical model, providing justification for the foundational assumptions, error estimates and validity limits. The model predictions will then be analyzed for the most intuitive physical understanding of the various effects. Numerical process models would be used to understand the effects on the model predictions of more realistic dissipation, boundary conditions and bottom topography. Finally, a regional numerical model will be used to attempt to reproduce observations in the ITF passages and explain these in terms of the underlying dynamics revealed by the more idealized models.Intellectual Merit: This study will advance the theory of geophysical fluid dynamics by clarifying the effects that sills in straits and channels have on the baroclinic structures and vertical propagation of incident coastal Kelvin waves.Broader Impacts: The Indonesian Throughflow is a vital link in the upper branch of the global oceanic overturning circulation, which in turn is an important component of Earth's climate system. The Indian Ocean Kelvin waves are known to episodically impact the ITF to the extent of frequently reversing the flow direction, yet the complex vertical and temporal structure of these effects is only now beginning to be understood and they are poorly parameterized in global models. Although this study does not aim at improving the parameterizations of global climate models, its contributions will at least improve the knowledge of what must be parameterized in order to successfully model the global system. The project will provide support for a graduate student and will train the student in analytical and numerical modeling techniques necessary to make further contributions in oceanic dynamics.