Impact of Nonlinear Barotropic Tides in the North Pacific

由于地球和月球运动引起的重力扰动，海洋中的每日表层潮汐对远洋和沿海环境中的生物、化学、地质和环流产生了深远的影响。随着潮汐模型的发展，人们认识到浅海和大陆架的潮汐之间的非线性相互作用(都是由远洋潮汐强迫的)导致能量回流到公海，但频率和波长发生了变化。这种能量流的影响不仅可以对全日和半日潮本身进行建模，而且可以对依赖于潮汐的现象(如深海混合)的能量学产生重大影响。这项研究探索了两条研究路线。第一个是确定沿海非线性潮汐在多大程度上“污染”通常被认为是远洋中的线性全日潮和半日潮。第二个问题是，沿海非线性潮汐能通量是否在比潮汐更短的时间，甚至短到15分钟的时间内，主导了整个海洋表层重力波运动的周期，这种可能性对海洋的能量收支和目前已知依赖这些波的其他地球物理现象(例如，地球的“地震嗡嗡声”；冰架的碎裂)都有影响。该项目涉及一名研究生的培训。这项研究的主要目的是利用观测工具阐明(1)远洋、正压、非线性潮汐的性质(例如，幅度、结构)，特别是在全日和半日潮汐带内；(2)远洋、正压、非线性潮汐能量的具体来源位置；(3)从主要的线性正压潮汐流向其他频带的重力波；(4)周期为15分钟至2小时的重力波能量的性质(如各向同性或非各向同性)和来源。这些目标将通过分析北太平洋现有的长达一年的海底压力记录来实现，这些记录很好地观测到了这些波浪和潮汐。这些方法包括最小二乘调和分析以及各种自谱和互谱技术，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.