Toward Operational Wave-Current Interactions Over the Agulhas Current System

A computationally inexpensive operational wave forecasting system taking wave-current interactions over the fast-flowing Agulhas Current into account is explored. Spectral wave model hindcasts at 1/16 of a geographical degree are employed using the Simulating Waves in the Nearshore (SWAN) wave model. Unidirectional wave-current coupling, with currents affecting waves, is performed using both Operational Mercator 1/12 degree (ORCA12) and GLOBCURRENT 1/4 degree currents. Comparisons between the coupled and uncoupled simulations indicate that wave amplification or lowering is highly dependent on the current magnitude and wave incident angle. In opposing current scenarios, the significant wave height can increase by 20-40% and by 60% in extreme cases. Model validation is performed using Jason-3 satellite altimetry measurements and in situ directional wave buoy measurements. The nearshore wave directional dispersion is found to be significantly influenced by the core of the Agulhas Current. This is especially prominent in current-following cases with wave-current direction differences of up to 20 degrees. The findings are all corroborated by simplistic, idealized models.