Mediterranean Tropical-Like Cyclones forecasts and analysis usingthe ECMWF Ensemble Forecasting System (IFS) with physical parameterizations perturbations.

Mediterranean Tropical-Like Cyclones, called "medicanes", present a multiscale nature and their track and intensity have been recognized as highly sensitive to large-scale atmospheric forcing and to diabatic heating as represented by the physical parameterizations in numerical weather prediction. Here, we analyse the structure and investigate the predictability of medicanes with the aid of the European Centre for Medium-Range Weather Forecast (ECMWF) Integrated Forecast System (IFS) ensemble forecasting system with 25 perturbed members at 9 km horizontal resolution (compared to the 16 km operational resolution). The IFS ensemble system includes the representation of initial uncertainties from the ensemble data assimilation (EDA) and a recently developed uncertainty representation of the model physics with perturbed parameters (Stochastically Perturbed Parameterizations, SPP). The focus is on three medicanes, Ianos, Zorbas and Trixie that have been among the strongest in recent years. In particular, we have carried out separate ensemble simulations with initial perturbations, full physics SPP, and with a reduced set of SPP, where only convection is perturbed to highlight the convective nature of medicanes. It is found that compared to the operational analysis and satellite rainfall data, the forecasts reproduce the tropical-like features of these cyclones. Furthermore, the SPP simulations compare to the initial condition perturbation ensemble, in terms of tracking, intensity, precipitation and more generally in terms of ensemble skill and spread. Moreover, the study confirms that similar processes are at play in the development of the investigated three medicanes, in that the predictability of these cyclones is linked not only to the prediction of the precursor events (namely the deep cut-off low) but also to the interaction of the upper-level dynamically driven Potential Vorticity (PV) streamer with the tropospheric PV anomaly that is driven by surface heating and stratiform and convective condensational heating. [ABSTRACT FROM AUTHOR]