Assessing the importance of deep ocean topographic scattering of low mode internal tides

尽管经过了几十年的研究，但关于低模态内潮的深海地形散射的重要性仍然存在许多模糊性。基于无穷小地形的理论研究预测散射效率为6-10%（Muller Xu 1992; StLaurent加勒特2002），最近的现场数据显示低模式内潮从夏威夷向东北方向的长距离传播（Zhao等人，2010）。然而，最近一项使用有限振幅随机地形的理论研究表明，散射可以为内潮提供快速衰减机制（Buhler& Holmes-Cerfon 2011），目前正在进行的NSF内潮散射（EXITS）现场计划实验研究主要集中在莱恩群岛脊，其中卫星测高数据表明，从夏威夷向西南传播的模式1通量中有37%被耗散（约翰斯顿，MerrfieldHolloway 2003&）该项目的智力价值在于提出和利用分析绿色函数法，对深海地形内潮散射作出合理预测。PI已经用于内部潮汐生成研究的方法不受以前理论方法的许多理想化的影响（例如，无穷小地形和/或恒定分层）。将通过与采用新型内部潮汐发生器的实验室实验进行比较来验证理论模型;已经进行了概念验证实验，以证明实验方案的可行性（Peacock等人，2010年）。这项工作将与NSF资助的EXITS计划的实地研究和数值模拟相结合。这项研究的主要影响是对低模式内潮的深海地形散射效率进行可靠的定量评估。经实验室实验验证的分析方法将为测试数值模型和解释现场数据提供基准;它还将被集成到一个名为iTide的MATLAB代码中，该代码将免费提供给海洋学家。该项目将支持一名博士后研究员和一名麻省理工学院本科研究员的培训。理论方法和实验结果将纳入研究生和本科生课程波动力学，流体力学和仪器。这项研究的结果将通过期刊文章，邀请研讨会和PI？的网站。将提议在白杨物理中心举办一个关于内波的讲习班。

Despite several decades of research, there is still much ambiguity about the importance of deep ocean topographic scattering of the low mode internal tide. Theoretical studies based on infinitesimal topography predict a modest 6-10% scattering efficiency (Muller & Xu 1992; StLaurent & Garrett 2002), and recent field data reveals long range propagation of the low mode internal tide northeast from Hawaii (Zhao et al. 2010). A recent theoretical study using finite-amplitude random topography, however, indicates that scattering can provide a rapid decay mechanism for internal tides (Buhler & Holmes-Cerfon 2011), and the currently underway NSF EXperimental study of Internal Tide Scattering (EXITS) field program is focusing on the Line Islands Ridge, where satellite altimetry data indicates 37% of the mode-1 flux propagating southwest from Hawaii is dissipated (Johnston, Merrfield & Holloway 2003).The intellectual merit of this project is in the advancement and utilization of an analytical Green function method to make reasonable predictions of topographic internal tide scattering in the deep ocean. The method, which the PI has already used for internal tide generation studies, is not subject to many of the idealizations of previous theoretical approaches (e.g. infinitesimal topography and/or constant stratification). The theoretical model will be validated through comparison with laboratory experiments that employ a novel internal tide generator; a proof-of-concept experiment has already been performed to demonstrate the feasibility of the experimental program (Peacock et al. 2010). The work will be integrated with the field studies and numerical simulations of the NSF-funded EXITS program.The primary broader impact of this research is a robust and quantitative assessment of the efficiency of deep ocean topographic scattering of low mode internal tides. The analytical method, validated by laboratory experiments, will provide a benchmark for testing numerical models and interpreting field data; it will also be integrated into a MATLAB code called iTide that will be made freely available to oceanographers. The project will support the training of a postdoctoral researcher and an undergraduate MIT researcher. The theoretical method and experimental results will be incorporated in graduate and undergraduate courses on wave mechanics, fluid mechanics and instrumentation. The results of this study will be disseminated through journal articles, invited seminars and the PI?s website. A workshop on internal waves at the Aspen Center for Physics will be proposed.