Topographic and frictional controls on tides in the Sea of Okhotsk

The sensitivity of barotropic tides to bottom topography and frictional parameters has been studied in a model for the Sea of Okhotsk. This region was chosen because of the paucity of bathymetry data and the possibility of using satellite altimeter data to better identify the bottom topography using variational inverse methods. The sensitivity was studied using both the direct and adjoint sensitivity. In the former approach, perturbations to the nominal model were applied to examine their impact; in the latter approach, the sensitivities were computed using the adjoint of the tangent linearization of the dynamical model. It is found that small-scale coastal near-resonant amplification controls the tidal dynamics, and the sensitivity of the solutions is dominated by topography in these regions, far exceeding the influence of other factors. Consequently, the tidal dynamics and resonant amplification creates a non-local relationship between water level and bottom topography and leads to a linear dependence of measurements upon a very few degrees of freedom. The results indicate severe limitations on inverse approaches for identification of topography, and add to the rationale for the collection and sharing of high quality bathymetry data to enable improved ocean modeling.