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Scientists at ESR, in collaboration with Oregon State University (OSU), run and update barotropic tide models for the Arctic Ocean and the seas surrounding Antarctica. There are two types of model: “forward” models based on numerical solution of the astronomically forced shallow-water wave equations; and “inverse” models that assimilate tide data to constrain the solution to match data within some prescribed error. While our long-term goal is to create accurate forward models, there is an immediate need for accurate tide models that are best achieved through data inversion.
Several models (listed below) are available to interested researchers. The model grid files are formatted to match the Oregon State Tidal Inversion Software (OTIS) format, and can be accessed using FORTRAN-based OSU Tidal Prediction Software (OTPS) code. ESR provides Matlab software, the Tide Model Driver (TMD) package, to access all the listed models and to make tidal predictions. TMD includes both a Graphical User Interface (GUI) and lower-level scripts. The TMD package is available following the links for model grids. See README_TMD.pdf for a detailed description of the software.
|Funded by NSF Polar Programs|
Model Comparisons to Altimetric and GPS-derived Elevation
The ocean tide models all report ocean tide, i.e., the variation about mean sea level of the height of the ocean surface relative to the seabed. For some applications, e.g., removing tide from satellite-derived altimetric heights (e.g., detiding of satellite-derived ice shelf elevation), an additional tide correction is required to account for the deformation of the solid earth by the water above it. This so-called “load tide” is, generally, roughly out of phase with the ocean tide, and a few percent of the ocean tide. The model, TPXO7.2_load, can be used to calculate load tides, which would then be added to the ocean tide prediction to give the complete tidal correction to altimetry.
Two things to note. (1) Because tide loading affects the Earth’s solid crust, it is non-zero even under continents, although it becomes very small tens of km inland from the coast. (2) Most satellite altimetry data sets already include tide corrections, including load tides. Make sure that you are not making tide corrections to data that have already been tide-corrected!
List of Models
Compatible Models from Oregon State University
The structure of the bathymetry and tidal harmonic coefficient grid files for the models available here are consistent with the Oregon State University suite of global and regional tide model solutions (see http://volkov.oce.orst.edu/tides/global.html and http://volkov.oce.orst.edu/tides/region.html). Thus, these models can also be run in Matlab with the TMD toolbox. Download the required model(s) from the OSU sites, then create a ‘Model’ file that names each of the necessary binary grid files. For example, the file, Model_tpxo7.2, is an ASCII file containing the following 3 lines:
These lines refer to the binary (OTIS format) files containing complex harmonic coefficient grids for height (h_tpxo7.2) and velocity (u_tpxo7.2), and the bathymetry grid file grid_tpxo7.2. For further information, see the README_TMD.pdf file.
ESR also carries out studies of baroclinic (depth-dependent) tides for specific high-latitude regions including the Ross, Scotia, and Weddell seas and specific Arctic regions.