Impact of Nonlinear Barotropic Tides in the North Pacific

由于地球和月球运动引起的引力扰动，海洋的日表面潮汐对海洋和沿海环境的生物、化学、地质和环流都产生了深远的影响。随着更精确的潮汐模型的发展，人们已经认识到，浅海和大陆架的潮汐之间的非线性相互作用（它们都受到远洋潮汐的影响）导致能量流回开阔的海洋，但频率和波长发生了变化。这种能量通量的影响不仅对日潮和半日潮本身的模拟产生重大影响，而且对依赖于潮汐的现象的能量学，如深海混合，也会产生重大影响。这项研究探索了两条研究路线。首先是确定沿海非线性潮汐“污染”了多少通常被认为是中上层海洋的线性日和半日潮汐。第二个解决的问题是，沿海非线性潮汐能量的通量是否在比潮汐周期短（甚至短至15分钟）的时间内主导了整个中上层海洋表面重力波运动，这种可能性对海洋的能量平衡和其他地球物理现象（例如，地球的“地震声”；冰架的破碎）都有影响，这些现象现在已知依赖于这些波。这个项目包括培训一名研究生。本研究的主要目标是利用观测工具阐明(i)远洋、正压、非线性潮汐的性质（例如振幅、结构），特别是在日潮和半日潮带内；（ii）远洋、正压、非线性潮汐中能量的具体来源位置；（iii）能量从主要的线性正压潮汐流向其他频段的重力波；（iv）周期为15分钟至2小时的重力波能量的性质（例如，是否各向同性）和来源。这些目标将通过分析北太平洋现有的长期（1年）底部压力记录来实现，这些记录可以很好地观察到这些波浪和潮汐。方法包括最小二乘谐波分析和各种自谱和交叉谱技术，其中一些技术借鉴了地震学。

The daily surface tides in the ocean, forced by gravitational perturbations arising from the motions of Earth and its Moon, exert a profound influence on the biology, chemistry, geology and circulation in both pelagic and coastal environments. As more accurate models of the tides have been developed, it has been realized that non-linear interactions among the tides in the shallow seas and continental shelves (which are all forced by the pelagic tides) result in a flow of energy back into the open ocean, but at altered frequencies and wavelengths. The impact of this energy flux can have significant consequences not only for modeling the diurnal and semi-diurnal tides themselves, but for the energetics of phenomena dependent on the tides such as abyssal mixing. This study explores two lines of research. The first is to determine how much the coastal non-linear tides "contaminate" what is generally considered to be the linear diurnal and semi-diurnal tides in the pelagic ocean. The second addresses the question of whether the flux of coastal nonlinear tide energy dominates the entire suite of surface gravity wave motions in the pelagic ocean at periods shorter than the tides, even as short as 15 minutes, a possibility that has ramifications both for the ocean's energy budget and other geophysical phenomena (e.g., Earth's "seismic hum"; fragmentation of ice shelves) that are now known to depend on these waves. The project involves training of one graduate student.The broad objectives of this study are to elucidate, using observational tools, (i) the nature (e.g., amplitude, structure) of the pelagic, barotropic, nonlinear tides, especially within the diurnal and semi-diurnal tide bands; (ii) the specific source locations for the energy in the pelagic, barotropic, nonlinear tides; (iii) the flow of energy from the principal, linear barotropic tides to gravity waves in other frequency bands; (iv) the nature (e.g., isotropic or not) and sources of the gravity wave energy at periods of 15 minutes to 2 hrs. These objectives will be accomplished by analyses of existing long ( 1 year) bottom pressure records in the North Pacific that well observe these waves and tides. The methodologies include least squares harmonic analysis and a variety of auto- and cross-spectral techniques, some borrowed from seismology.