Impact of Sea Surface Temperature on COSMO Forecasts of a Medicane over the Western Mediterranean Sea

The paper describes and analyzes the sensitivity of an ope rational atmospheric model to different SST (sea surface temperature) estimates. The model’s sensitivity has been analyzed in a Medicane (Mediterranean hurricane) test case. Numerical simulations have been performed using th e COSMO (consortium for small- scale modeling) at mospheric model, in the COSMO-ME configuration. The model results show that the model is capable of capturing the position, timing and intensity of the cyclone. Sensitivity experiments have been carried out using different SSTs surface boundary conditions for the COSMO forecasts. Four different experiments have been carried out: the first two usi ng SST fields obtained from the OSTIA (operational sea surface temperature and sea ice analysis) system, while the other two using the SST analyses and forecasts from MFS (Mediterranean Forecasting System, Tonani et al., 2015; Pinardi and Coppini, 2010). The different boundary conditions determine differences in the trajectory, pressure minimum and wind intens ity of the simulated Medicane. The sensitivity experiments showed that a colder tha n real SST field determines a weakening of the minimum pressure at the vortex center. MFS SST analyses and forecasts allow the COSMO model to simulate more realistic minimum pressure valu es, trajectories and wind speeds. It was found that MFS SST forecast, as surface boundary conditions for COSMO-ME runs, determines a significant improvement, compared to ASCAT observations, in terms of wind intensity forecast as well as cyclone dimension and location.