Shallow and deep water global ocean tides from altimetry and numerical modeling

We present here a 1/4 degrees resolution near-global barotropic tidal model designed specifically to provide more accurate tides in shallow water. The model assimilates tides derived from 4 years of TOPEX/Poseidon (T/P) altim etric data. Procedures are used that tend to preserve the small spatial sca les in the tidal structure in shallow water. Data from coastal tide gauges are also assimilated into the model. The result; is a tidal model that is u seful in most of the shallow and deep areas of the global oceans. Some prob lems exist in regions where no data are available for assimilation, such as the Southern Ocean. Pelagic tide gauge comparisons show that in deep water the new model is comparable in accuracy to the best of the existing T/P-ba sed global tidal models. Comparisons to crossover differences in shallow wa ter suggest improved performance. We found that more accurate accounting of the load tides in the ocean tide model using an iterative technique leased on the Green's function formalism does not yield ocean tides that are sign ificantly different from the simpler approaches used thus far by ocean tide modelers when data are assimilated. It is our hope that this tidal model w ill not only help advance our understanding of shallow water tidal processe s around the globe but also extend the utility of altimetry to waters shall ower than 1000 m.