Added Value of Using Atmosphere-Ocean-Wave Coupled Modelling System on Mediterranean Tropical-like cyclones

Abstract:

The devastating Mediterranean tropical-like cyclones characterized by strong winds, low pressure centers and extreme precipitation are called medicanes. These severe weather phenomena threaten the coastal regions and small islands in the Mediterranean. The rare nature of these events leaves some processes unresolved. Therefore, better understanding of the feedback mechanisms between the atmosphere and the sea is necessary to enhance our knowledge regarding the unresolved processes and evolution of these extreme phenomena. In pursuing these mechanisms, we used state of the art Regional Earth System Model (RegESM; Turuncoglu and Sannino, 2017) that allows to combine atmosphere, ocean and wave models. Based on literature and available remote sensing products, we selected 16 medicane cases for the performance evaluation of the high-resolution standalone atmosphere, the coupled atmosphere-ocean and the fully coupled atmosphere-ocean-wave simulations. The simulations have been performed for the 1979-2012 period over the Med-CORDEX domain prescribed under the CORDEX (Coordinated Regional Climate Downscaling Experiment) framework. The novelty of this study is that the atmosphere-ocean-wave simulation we performed is the first wave coupled long-term simulation for the Med-CORDEX project. Applying this coupled model showed that the interaction among ocean, waves, and atmosphere have a strong influence on medicane dynamics with coupled simulations improving the accuracy of wind speed and direction. The reason behind this better replication of the medicanes with the coupled model is the wave model’s interactive contribution with the roughness length to the surface winds, which decreases the wind speed and allows medicane intensification through the more realistic heat and momentum exchange between the surface components of the models. On the other hand, the spatial extent and the timing of the observed medicanes are better simulated by both coupled simulations. In some cases, two coupled simulations produce higher sea surface temperature which enhances the evaporation and fuels the storm by the increased heat and momentum fluxes. In conclusion, the recently developed modeling system RegESM is better capable to improve the understanding of the mechanisms driving medicanes.