Breaking internal tides are known to be a major driver of deep-ocean diapycnal mixing. However, much of the energy input into them is in the first few modes, which can propagate 1000's of kilometers before breaking. As a result, little is known about where and how they break, in spite of the known sensitivity of global circulation models to the geography of mixing. Therefore, this study will construct a global map of low-mode internal tide energy flux and dissipation by application of state-of-the-art techniques to a combination of satellite altimetry, moorings, and a numerical model. The approach captures both the non-uniform barotropic-to-baroclinic tide conversion near rough topography as well as patchiness due to the non-uniform dissipation of low-mode internal tides.
The global coverage of satellite altimeters makes them the only practical observational tool available for the task. However the poor spatial resolution of any single satellite, and the inability of altimetry to detect temporally incoherent signals, have hampered the interpretation of past altimetric estimates of low-mode internal tide energy and energy flux. This study addresses these shortcomings in order to produce the needed global maps: (1) To address the low-resolution problem, the team will expand on their previous work (in which they used the T/P-Jason tandem mission) by combining multiple satellite altimetric data from T/P- Jason, T/P-Jason tandem, GFO, and ERS. The multi-satellite technique was recently demonstrated in the North Pacific, and showed that spatial resolution is improved to the point where the altimetric estimates agree with high-resolution numerical models. (2) To understand the loss of coherence of internal tide propagating in an ever-changing ocean, the PIs will analyze a new high-resolution global simulation that includes a realistic internal tide field as well as realistic meso- and large-scale ocean circulations. The model estimate of how the non- uniform moving ocean makes internal tide incoherent will be validated by the analysis of several long moored time series collected around the globe.
With these improvements, the techniques should now be up to the task of mapping the low-mode internal tide's energy flux and dissipation on the globe. In doing so, this project will lead to a better understanding of the processes that affect the propagation and dissipation of internal tide on a global scale.
Broader Impacts: The primary broader impact of this work will be an improved understanding and a parameterization of the magnitude and geography of dissipation, of known importance to general circulation models. In addition, the team will provide maps of altimetrically-observed internal tide quantities to all researchers as well as the public via a website and/or direct communication with the PI's. In addition to being of great use in planning experiments, such maps will be of relevance for a variety of physical and biogeochemical studies. The maps and the model simulations will be used in community outreach programs such as APL's K-12 volunteer list and Seattle's Pacific Science Center. The study will also educate three undergraduate students as part of the Washington Space Grant program, a joint program between Washington State and NASA seeking to encourage students at the University of Washington to pursue science careers.