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 simulations are performed using the ENEA-REG regional Earth system model at 12 km atmospheric horizontal resolution over the Med-CORDEX domain, both driven by ERA5 reanalysis, for a common 33-year period (1982–2014). The atmosphere stand-alone simulation uses the WRF model with prescribed ERA5 SST, while in the second WRF is coupled to the MITgcm ocean model at horizontal resolution of 1/12°. A cyclone track method, 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 most impactful, cyclones. Results show that the seasonal and spatial distribution of the 500 most intense cyclones is similarly reproduced between WRF and ERA5, regardless the use of the 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 throughout the boundary layer. Additionally, the research investigates the 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 effectiveness of the coupled model in representing dynamic and thermodynamic processes associated with extreme cyclones across both the atmosphere and the ocean.