Impact of the Ocean-Atmosphere coupling on extratropical cyclones around the Mediterranean basin

The Mediterranean basin is well recognized as one of the main climate change hotspots; besides, this region is one the most active cyclogenetic area of the Northern Hemisphere with a large number of intense cyclones occurring every year mainly during winter and fall. The climatology of Mediterranean cyclones has been deeply investigated in the past years, leading to a high agreement on the tracks density, seasonal cycle and favorite locations of cyclogenesis. Nevertheless, open questions still remain on the future evolution of Mediterranean cyclogenesis and associated impacts. Mediterranean cyclones typically present weaker intensities, smaller sizes and shorter lifetimes than tropical cyclones or other mid-latitude cyclones that develop over open oceans. However, they are often responsible for extreme precipitation and wind events leading to severe socio-economic and environmental impacts especially over densely populated regions and coastal areas. Thus, studying the feedbacks of air-sea interactions on Mediterranean cyclones will bring to a better understanding of both the contribution of cyclones to the variability in and extremes of the regional climate and the impacts on the marine ecosystems as well as the associated risks in maritime transportation and coastal structures.

This study aims to investigate the added values of the ocean-atmosphere coupling in regional climate models in reproducing Mediterranean cyclones. To this end, two simulations are performed using the ENEA-REG regional earth system model at 12 km over the Med-CORDEX domain. The first experiment uses the mesoscale WRF model with prescribed Sea Surface Temperature (SST), while in the second WRF is coupled to the MITgcm ocean model. Different tracking methods, based on sea level pressure, are used to account for the uncertainties linked with mathematical and physical definitions of cyclone itself. The simulations are validated against ERA5 reanalysis dataset in terms of their ability to reproduce the Mediterranean cyclone climatology as well as to represent sub-daily fields linked to the cyclones (e.g. SST, heat fluxes, wind, precipitation). Here we show how the coupling of the atmosphere with an interactive ocean model affects the number of cyclones along with their intensity and duration.