Coupling of the Regional Ocean Modeling System (ROMS) and Wind Wave Model

In this work the structured grid circulation model ROMS is coupled with the unstructured grid Wind Wave Model II. The physics of the model have been completely reformulated using Vortex Force formalism. The surface stress is consistently computed from the wave model. The chosen models and coupling approach, allows the grids of both models to be chosen independently. However, we also introduced a systematic approach of generating unstructured grids from finite difference grids, while preserving the structure of the flow near islands and coasts. The influence of different wave model grids on the coupling was investigated and found to be quite small, whereas the computational time can be drastically reduced. A new parallel coupling library was developed in order to couple the models. The benefit of the new coupling library is that it gives an almost optimal data exchange between different domain decomposition originating from the different discretization/parallelization of the different models. The coupled modelling system was validated on the analytical test case of the radiation stress induced wave setup. Finally, the coupled model was applied to the Adriatic Sea to investigate the wave-current dynamics during a bora and a sirocco event. The model was forced using data from the ALADIN atmospheric model. As a possible source of error model wind field was validated against QuikSCAT data and ENVISAT data indicating that ALADIN wind speeds are likely underestimated. Consistently the wave model, shows a negative bias with respect to the in situ measurements and altimeters but producing overall comparable results as in previous studies. The influence of the currents was evaluated with respect to significant wave height and zero down crossing periods, revealing strong interactions especially in the regions of strong current gradients as e. g. observed in the north and south-Adriatic gyre systems. The modulations based on the given setup show up to 10% variations during the subsequent events. (C) 2013 Elsevier Ltd. All rights reserved.