Vertical mode structure functions are computed over the entire tropical Pacific Ocean (30¿N to 30¿S) by using the Levitus temperature-salinity climatological file and a National Oceanic and Atmospheric Administration bathymetry file and over a few selected areas of the Pacific by using a more accurate conductivity-salinity temperature depth (CTD-STD) file. At every 1¿ grid point of the tropical Pacific, phase speeds of the first five modes are estimated from the Levitus density profiles and the actual bottom depth. They range from 305 to 195 cm s-1 for mode 1 to 65 to 40 cm s-1 for mode 5. Because of the coarse vertical resolution in the Levitus profiles, the corresponding phase speeds are underestimated by about 8% compared to phase speeds calculated with CTD-STD profiles. In order to estimate the relative importance of density stratification and bottom depth on vertical mode structure functions, two sets of modes are calculated. The first set is calculated with the Levitus density profiles truncated or extended to a mean basin bottom depth (3570 m) at every grid point. The resulting modes are representative of the influence of density stratification on modal calculations. The second set is computed with a mean basin density profile and the actual bottom depth at every grid point. This set represents the influence of bottom depth. Phase speed comparison between these two sets of modes and the original modes indicates that for the first two modes, the bottom depth contribution is an order of magnitude less than the density contribution.

For modes 3 and 4, the bottom depth contribution increases, and for mode 5 it is almost equal to the density contribution. The relative importance of deep density stratification and upper layer stratification on vertical mode structure functions is evaluated by using the more accurate CTD-STD file. This study is restricted to a few small areas with enough deep profiles, taken within a few days, to ensure proper statistical results. Vertical modes are calculated first with complete vertical density profiles and then with the same profiles truncated at a certain depth and replaced below by a mean density profile (obtained from 159 CTD-STD deep profiles in the tropical Pacific). Statistical comparison reveals that meaningful computation of the first five vertical modes can be obtained in the tropics by using precise density information in the first 600 m and mean density information below. ¿ American Geophysical Union 1993