Empirical internal tide models from past multisatellite altimeters are the only observational and currently the most reliable models. However, all current altimeter-based internal tide models represent the ~20-year-long coherent component and miss the incoherent component. Thus, extracting the time-variable internal tide from satellite altimetry is a challenging and rewarding question. We take up this challenge by developing and improving a plane wave fit method. In this method, internal tides are extracted in two-dimensional fitting windows, rather than at individual sites. This approach is superior to point-wise harmonic analysis because it enables us to resolve multiwave interference and extract internal tides in short time windows. Our analyses in several regions reveal significant seasonal and interannual variations, which in turn confirm the necessity and feasibility of exploring the incoherent internal tide. Using this method, we are constructing global internal tide models for all principal tidal constituents, and for each tidal constituent we are constructing climatological monthly and annual fields using subsetted altimeter data.

Our work inspires two new concepts: next-generation internal tide model and internal tide oceanic tomography (ITOT). First, next-generation internal tide models that resolve seasonal and interannual variations are being developed. Our new models have time-varying amplitude and phase, in contrast to time-invariant harmonic constants in barotropic tide models and current internal tide models. Our new models will be evaluated using in situ moorings and independent altimeter data. Second, we are using our models to develop a new tomographic technique, ITOT, for monitoring global ocean change by tracking long-range internal tides. ITOT is similar to acoustic tomography, but the working waves are internal tides instead of sound. Ocean warming/cooling thus can be monitored using satellite altimetry by precisely measuring changes in the propagation speed of internal tides. This technique will be evaluated using Argo data and the ECCO2 estimates. ITOT may offer a long-term, cost-effective, environmentally-friendly technique for monitoring global ocean change and variability.