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.
