engleski

Analysis of Imposing Tidal Dynamics to Nested Numerical Models

Tides often play an important role in the circulation of coastal and shelf environments. In numerical modeling, high- resolution models are used for these regions requiring that they be nested in coarser models with properly specified tidal boundary conditions. In this paper, we examine two, one-way nesting methods for specifying the combined baroclinic and barotropic tides to a child model: i) specifying spatially interpolated boundary values from the outer model at a specified interval ; and, ii) using the same boundary conditions as (i), but fitting and removing the tidal harmonics from the boundaries and providing the harmonics as separate forcing. We compare these methods in two regions: an idealized seamount experiment where baroclinic tides are generated outside of and propagate into the nested domain ; and, a realistic case of the Hawaiian archipelago with strong barotropic tides with significant energy conversion to the baroclinic tide both inside and outside of the nested domain. In all cases, we find that there is significant improvement in the tidal dynamics by removing the tides from the boundary conditions and using a separate tidal forcing as compared to simply prescribing the boundary conditions. Furthermore, because many numerical models use temporal linear interpolation for boundary conditions at each time-step, if the tidal function is not specified separately, the amplitudes are significantly reduced and --- more importantly --- energy is aliased at higher frequencies. These findings are applicable to any tidally energetic region (particularly shelf and coastal systems) and become more significant with nonlinear interaction between tidal constituents.

Internal tides ; Nested Models ; Boundary Conditions ; ROMS model ; Hawaii

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