Efficiently Incorporating Baroclinic Effects in a Global, Depth-Averaged Storm Tide Model

With the growing frequency of storm tide events, emphasis has been placed on increasing the accuracy of total water level (TWL) predictions of both hindcasts and forecasts of coastal flooding due to tropical and extratropical storms. While global, barotropic TWL models have become incredibly accurate, they fail to capture density driven, baroclinic effects which can have dramatic effects on coastal water levels. This study examines a loose, one-way coupling between a global, depth-resolving, ocean circulation model (OGCM) and a high-resolution, global, depth-averaged TWL system. By calculating density-driven effects on coarsely resolved OGCM and using them as forcing in a high-resolution TWL model, it is possible to capture baroclinic effects in a computationally efficient manner. This coupling has strong effects on global circulation and greatly improves the representation of deep-ocean currents in the barotropic model. It is shown that the inclusion of baroclinic effects in this manner greatly improves the accuracy of total water level predictions of the global model, better captures the power spectra of water levels at measuring stations, and captures the seasonality of density-driven effects. Additionally, the coupling has powerful effects on internal tide generation due to barotropic to baroclinic conversion. The parameterization of this phenomena-which is driven by tidal currents crossing over steep bathymetry in the deep ocean and at shelf breaks-is modified to preserve the total tidal dissipation in a purely barotropic tidal model. The preservation of this tidal dissipation mechanism ensures that global tides are still accurately resolved with minimal alteration to tuning coefficients of the parameterization.