Coupling ocean currents and waves for seamless cross-scale modeling during Medicane Ianos

Abstract. This study investigates the effects of a two-way wave-circulation coupled modeling framework during extreme weather events, with a particular focus on Medicane Ianos, one of the most intense cyclones occurred in the Mediterranean Sea. By utilizing a high-resolution unstructured numerical grid, the study explores wave-current interactions in both open ocean and coastal environments. To this scope, we developed the first external coupler dealing with the SHYFEM-MPI circulation model and the WAVEWATCH III wave model. The interactions considered in this framework include sea-state dependent momentum flux, radiation stress, Doppler shift, dynamic water depth for waves, and effective wind speed. The study adoptes a rigorous validation of the formulations using idealized benchmarks tailored for these specific processes. Afterwards, the modeling framework was employed in real-case simulations of Medicane Ianos. The model is calibrated, and the ocean variables are rigorously validated against in-situ and Earth Observation (EO) data, including satellite-based measurement. The study found that wave-induced surge components contribute from 10 to 30 % of the total water level during the storm, and that sea-state dependent momentum during a Medicane can influence the vertical structure of the ocean up to 100 m. The accuracy of the wave model improves by around 3 % in terms of RMSE when coupled with a circulation model.

This study underscores the importance of such coupled models in accurately forecasting Medicanes, storm surges, and their impacts, particularly as climate change intensifies extreme events in the Mediterranean Sea.