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，通常被认为是海面规则的上升和下降，大约一米。当这些潮汐与地形相互作用时，就会产生内潮，在内潮中，海洋内部的水可能会在100米以上涨落。当这些大幅度波破裂时，它们会耗散能量，这些能量对推动世界海洋的大范围环流起到了作用。由于波浪在海洋盆地中传播的距离很长，它们为潮汐能提供了一种手段，使潮汐能在远离最初转化为内波的地区可用。近年来，已经有几个主要的野外实验(HOME和IWAP)，目的是追踪这些内部潮汐形成和传播离开夏威夷的过程。数值模式表明，这些内潮汐在长时间内是稳定的。它们可以通过卫星测高观测到，但到目前为止，这些潮汐分析都是在个别地点进行的。在目前的研究中，将使用一种新的卫星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海洋学家，他将使用频率-波数分析，利用TOPEX/Poseidon数据得出潮汐调和常数，该数据在1992年至2005年的13年间几乎覆盖全球。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，关于这一现象的观测证据很少。这项研究的一个主要目标是得出该纬度附近任何增强的耗散的定量测量。此外，这项研究将更好地量化这些内部潮汐的整体消散尺度。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础物理有影响。因此，这项研究可能会影响这些系统的数值建模方式。

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.