Numerical simulations of ocean surface waves along the Australian coast with a focus on the Great Barrier Reef

Numerical simulations of ocean surface waves along the Australian coast are performed with the spectral wave model WAVEWATCH III (WW3) and the state-of-the-art physics and numerics. A large-scale, high-resolution (1–15 km) unstructured mesh is designed for better resolving the extensive Australian coastline. Based on verification against altimeter and buoy observations, it is found that the WW3 simulations, with an observation-based source term package (i.e., ST6) and other relevant physical processes, perform reasonably well in predicting wave heights and periods in most regions. Nonetheless, the Great Barrier Reef (GBR) represents a challenging region for the wave model, in which wave heights are severely overestimated because most of the individual coral reefs and their strong dissipative effects could not be resolved by the local mesh. A two-step modeling strategy is proposed here to address this problem. First, individual coral reefs are regarded as unresolved obstacles and thus complete barriers to wave energy. Second, we adopt the unresolved obstacles source term proposed recently to parameterize the dissipative impact of these subgrid coral reefs. It is then demonstrated that this subgrid-scale reef parameterization enhances the model performance in the GBR dramatically, reducing the wave height bias from above 100 % to below 20 %. The source term balance and the sensitivity of model results to the grid resolution around the GBR are also discussed, illustrating the applicability of this two-step strategy to km-scale wave simulations.