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有规律的上升和下降。这些潮汐，当它们与地形相互作用时，产生内部潮汐，在这种情况下，海洋内部的水可能会上升和下降超过100米。当这些振幅较大的波浪破裂时，它们会耗散能量，而这些能量在推动世界海洋的大规模环流中起着作用。由于波浪在海洋盆地中传播很远的距离，它们为远离最初转化为内波的地区提供了一种利用潮汐能的方法。近年来，有几个主要的野外实验（HOME和IWAP）旨在追踪这些内部潮汐的形成和从夏威夷传播出去。数值模型表明，这些内部潮汐在很长一段时间内是稳定的。它们可以通过卫星测高观测到，但迄今为止，这些潮汐分析都是在个别地点进行的。在目前的研究中，将使用一种新的基于卫星的测高数据分析来跟踪内部潮汐。首席研究员是华盛顿大学的一名海洋学家，他将利用TOPEX/Poseidon数据进行频率波数分析，得出潮汐谐波常数。TOPEX/Poseidon数据覆盖了1992年至2005年13年间的全球范围。最近的理论工作表明，在28.9度的临界纬度有增强的耗散。然而，几乎没有观测到这一现象的证据。本研究的一个主要目标是推导出该纬度附近任何增强消散的定量测量。此外，该研究将更好地量化这些内部潮汐耗散的总体规模。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具有启示意义。因此，这项研究可能会影响这些系统的数值模拟方式。

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.