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2.3.1 Bottom Topography

Bottom depth is one of the most important parameters for a realistic ocean model. Bottom depth is derived from acoustic soundings from a ship. Naturally, all ocean basins are not covered equally well. Regions near coasts of well-developed countries such as the U.S. and regions well-traversed by ships are covered reasonably well, while vast areas of the southern hemisphere are not explored very well. Very high resolution (approaching 1 km) bottom topography is generally not available in the public domain. The best resolution public domain topography thus far is the gridded ETOP05 data base at the National Center for Atmospheric Research (NCAR), which contains 5 min (roughly 9 km) resolution of Earth's topography (including land). This data base is generally adequate for deeper parts of the ocean, but is less reliable over continental shelves (<200 m deep). Nevertheless, for most ocean models it suffices. Provided is a program to derive topography for any region delineated by the latitude--longitude limits and at any desired grid resolution. The program averages the depths available from the data base in each model grid. Another topographic data set is the DBDB-5 (Digital Bathymetry Data Base at 5 min intervals), developed by the U.S. Naval Oceanographic Office in about 1982. Below are figures illustrating some topographically interesting oceanic areas from around the world. These figures were created using data sets like the ones mentioned above.

Figure 6: Ocean Depth Surrounding the Aleutian Islands.

Figure 7: Ocean Depth Surrounding the Hawaiian Islands.

Figure 8: Ocean Depth Surrounding the Mariana Islands.

Figure 9: Sea of Japan Topography.

Basin geometry, another important factor in ocean modeling, is derived from the topographic data sets, which usually have default values of, for example, for the land points.

(See exercises 7 and 7.)