Modeling ocean tides with and without assimilating data

Abstract

When reviewing the application of semiempirical and free ocean tide models to the computation of semidiurnal, diurnal and long‐period tides, it is recognized that the basin dominating features of the computed oscillation systems have in general proven to be compatible with the relevant data available. In particular, free tidal models moreover allow, together with the results from investigations of free oscillations and of tides in idealized ocean basins, to determine the dependence of tidal regimes on specific constituents of tidal dynamics, e.g., on loading and self‐attraction. As the computational results are not as precise as required for, for example, geophysical and astronomical applications, a procedure has been developed permitting to utilize also the increasing amount of information from pelagic data for improving the mapping of ocean tides by numerical models. Using a spectral model, test calculations have first been performed for an idealized ocean basin with well‐determined free and forced oscillation properties. Reference is made in detail to a realistic ocean tide model which includes loading and self‐attraction using a convolution integral and which permits the assimilation of data by minimizing a functional made up by the residuals of data and of equations of momentum. Consistent fields of sea surface elevation and currents, with mass precisely conserved, have been obtained for the M2 tide in the world ocean. Comparisons are drawn between these fields and those having been obtained by applying that free model which represents a special case of the model considering information from data. The gain of the tidal oscillation system in basin wide realism due to assimilating pelagic harmonic constants is estimated and found promising.