Extreme Mediterranean cyclones and associated variables in an atmosphere-only vs. an ocean-coupled regional model

Abstract. Complex air–sea interactions play a major role in both the variability and the extremes of the Mediterranean climate. This study investigates the differences between an atmosphere-only and an ocean-coupled model in reproducing Mediterranean cyclones and their associated atmospheric fields. To this end, two climate simulations are performed over the Mediterranean basin, both driven by the ECMWF ERA5 reanalysis, for a common 33-year period (1982–2014). The atmosphere standalone simulation uses the Weather Research and Forecasting (WRF) model with prescribed ERA5 sea surface temperature (SST), while in the second experiment WRF is coupled to the Massachusetts Institute of Technology General Circulation Model (MITgcm). A cyclone-tracking algorithm, based on sea level pressure, is applied to both simulations and to the ERA5 reanalysis to assess the model capability to reproduce the climatology of intense, potentially greatly impactful cyclones. Results show that the seasonal and spatial distribution of the 500 most intense cyclones is similarly reproduced between WRF and ERA5, regardless of the use of coupling. The two simulations are then compared in terms of sub-daily fields at the cyclones' maximum intensity. Differences in SST distribution between the models primarily control variations in atmospheric variables, not only at the surface but also throughout the planetary boundary layer, due to the mixing by the turbulent processes, enhanced during intense cyclones. Additionally, this research investigates cyclone effects on ocean properties in the coupled simulation, revealing that strong winds enhance surface heat fluxes and upper-ocean mixing while lowering SST. The analysis shows the ability of the coupled model to coherently represent the dynamic and thermodynamic processes associated with extreme cyclones across both the atmosphere and the ocean.