The introduction of observation-based wave physics into the wind-wave model WAM: Wave assessments for a semi-enclosed basin

Abstract

This study presents the successful integration of ST6 observation-based source term physics into the WAM Cycle 7 wind-wave model, marking the first comprehensive validation and comparison with the existing wave physics ST3 and ST4 of WAM, with a specific focus on the Black Sea. Overall, validations demonstrate consistent and satisfactory performance across all three source term physics, aligning with findings from previous studies using different wave models in various regions. Minor discrepancies exist. ST3 excels in representing significant wave height, crucial for wave power applications, while ST4 and ST6 best reproduce T_M02 mean wave period and mean wave direction, impacting Stokes drift direction and thereby drift simulations. Validation metrics unaffected by bias confirm the similarity of the three physics, ruling out calibration issues. Evaluations of ERA5 wind forcing reveal larger errors induced by wind compared to source terms, emphasising the significance of wind quality and model calibration over physics choice. During extreme events, the physics exhibit similar performance, although wind speeds remain relatively low compared to the global ocean. Studies indicate greater discrepancies among physics in larger-scale scenarios with increased fetch, prevailing swell, or hurricanes, where ST6 demonstrates superior performance, while ST4 fares better in low-wind conditions. These findings showcase the need for the examination of these scenarios in the new WAM Cycle 7 version.