A sensitivity analysis with COSMO-LM at 1 km resolution over South Italy

Abstract

The results of a sensitivity analysis based on COSMO-LM (COnsortium for Small-Scale MOdeling-Lokal Model) simulations driven by ECMWF-IFS (European Centre for Medium-Range Weather Forecasts-Integrated Forecasting System). global data over a domain located in southern Italy are presented. Simulations have been performed at very high resolution (about 1 km). The main aim of this study is to individuate the most sensitive physical and numerical parameters of the model configuration, comparing a set of 18 simulations in terms of temperature and precipitation against ground observations. The parameters that result in having more influence for a proper representation of temperature and precipitation fields are the heat resistance length of laminar layer (which accounts for the high complexity of the interaction of the atmosphere with the underlying surface) and the minimal diffusion coefficient for heat. Temperature values are strongly influenced also by the vertical variation of critical relative humidity. An optimized tuning of these parameters allows COSMO-LM to improve the representation of simulated main features of this area, with significant bias reductions.