Investigating ocean stratification changes with global warming by long-range internal tides

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Stratification is a key property of the ocean and plays an important role in almost all ocean processes including mass transport, vertical mixing and overturning circulation. It is of high priority to monitor its seasonal cycle, decadal trend and interannual variation on the global scale. Long-range internal tides, which attribute their existence to ocean stratification, are a natural choice for monitoring ocean stratification changes. This project will further mature a technique to accurately observe low-mode internal tides using satellite altimetry. It will not only improve our understanding of internal tide activities, but also develop a new technique for monitoring ocean stratification, providing an independent long-term, low-cost, environmentally-friendly observing system. The global ocean is subject to changes as evidenced by frequent extreme weathers such as heat waves and tropical cyclones. Besides ocean warming and sea level rise, it is well-known that stratification intensification may change large-scale ocean circulations; one extreme scenario is shown in the movie “The Day After Tomorrow.” The satellite-derived internal tide models will be useful to the oceanographic community in designing field experiments, modeling internal tides, primary productivity, ocean acoustics, coral reef bleaching, ocean mixing, and internal tide correction. The new information on ocean stratification changes will be made freely available to researchers around the globe. This project will train a graduate student at the University of Washington. The team will also make an animation to simply explain the techniques to young kids and the public.Ocean stratification plays an important role in many dynamics processes including mass transport, isopycnal mixing and meridional ocean circulation. This project will investigate ocean stratification changes using satellite altimetry, the World Ocean Atlas, Argo floats, and two numerical models ECCO and HYCOM. Its goals are to (1) construct a global network utilizing long-range internal tide beams, (2) quantify seasonal cycle, decadal trend, and interannual variation of ocean stratification in terms of internal tide speed, (3) validate the satellite-derived ocean stratification changes with in situ measurements, and (4) evaluate the performance of ECCO and HYCOM in reproducing ocean stratification.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.