Internal Tides, Altimetry and the Subtropical Catastrophe: A Global Search for Loss of Low-Mode Internal Tide Energy at 28.9 degrees Latitude

潮汐是由太阳和月亮的引力引起的，通常被认为是海面大约一米的规则升降。当这些潮汐与地形相互作用时，会引起内潮，其中海洋内部的水可能会上升和下降超过100米。当这些大幅度的波浪破碎时，它们会耗散能量，这在驱动世界海洋的大规模环流中发挥作用。由于波浪在海洋盆地中传播很长的距离，它们提供了一种方法，使潮汐能在远离最初转换为内波的地区得到利用。近年来，有几个主要的现场实验（HOME和IWAP），旨在跟踪这些内潮，因为它们形成和传播远离夏威夷。 数值模型表明，这些内潮在很长一段时间内是稳定的。它们可以通过基于卫星的测高技术进行观测，但迄今为止，这些潮汐分析仅在个别地点进行。在本研究中，将使用对卫星测高数据的新分析来跟踪内潮。主要研究员是华盛顿大学的海洋学家，他将利用1992年至2005年期间覆盖全球的TOPEX/Poseidon数据，利用频率-波数分析推导潮汐调和常数。最近的理论工作表明，在28.9度的临界纬度上有增强的耗散。然而，这种现象的观测证据很少。这项研究的一个主要目标是获得一个定量的措施，任何增强耗散在这个纬度附近。此外，这项研究将提供一个更好的量化的整体规模的耗散这些内部潮汐。 这项研究对控制大规模海洋环流如何影响地球气候系统的基本物理学有影响。因此，这项研究可能会影响这些系统的数字建模方式。

Tides, which are caused by the gravitational pull of the sun and the moon, are commonly thought of as the regular rise and fall of the sea surface of approximately a meter. These tides, when they interact with topography, give rise to internal tides, in which water in the interior of the ocean may rise and fall over 100 meters. When these large amplitude waves break, they dissipate energy which plays a role in driving the large scale circulation of the world's ocean. Because the waves propagate long distances across ocean basins, they provide a means for tidal energy to be made available in regions far from where it was initially converted to internal waves. In recent years, there have been several major field experiments (HOME and IWAP) which aim to track these internal tides as they form and propagate away from Hawaii. Numerical models have shown that these internal tides are stable over long periods. They can be observed by satellite-based altimetry but to date these tidal analyses have been at individual locations. In the present study, internal tides will be tracked using a new analysis of satellite-based altimetry data. The principal investigator, an oceanographer at the University of Washington, will use frequency-wavenumber analyses to derive tidal harmonic constants using the TOPEX/Poseidon data which has near global coverage over a span of thirteen years, between 1992 and 2005. Recent theoretical work has suggested that there is enhanced dissipation at the critical latitudes of 28.9 degrees. However there has been little observational evidence of this phenomenon. A major goal of this study is to derive a quantitative measure of any enhanced dissipation near this latitude. In addition, the study will provide a better quantification of the overall scales of dissipation of these internal tides. The study has implications on the basic physics that governs how the large-scale ocean circulation affects the Earth's climate system. Consequently, the study could influence how these systems are modeled numerically.