Implementation and evaluation of aerosol and cloud microphysics in a regional climate model

A new aerosol modeling framework is presented within the regional climate model COSMO‐CLM. The model accounts for the microphysical interactions of internally and externally mixed aerosol particles. Sulfate, black carbon, particulate organic matter, sea salt, and mineral dust are considered. The model is applied over Europe at a horizontal resolution of 50 km. The lateral boundary conditions are given by the ERA‐Interim reanalysis for the meteorological fields and by a global ECHAM5‐HAM simulation for the aerosols. Present‐day AeroCom emissions are used for the evaluation period from 1997 to 2003. The model largely reproduces the annual mean pattern of the aerosol optical depth derived from satellite data over Europe (model and observed domain mean is 0.17, but it is 0.37 with standard model version). The annual cycle is overestimated in COSMO‐CLM in some regions due to strong dust transport across the Mediterranean in late spring. Day‐to‐day variability in aerosol optical depth and the Angstrom exponent is also captured by the model. The corresponding correlations of the daily mean time series between measurements from AERONET stations and the model range from 0.17 to 0.74. In comparison with the standard model version, which does not account for aerosol transport and indirect aerosol effects and uses an outdated aerosol climatology, the mid‐European summer cold bias disappears with the new framework. The new framework allows studies of mesoscale interactions between aerosols, clouds, precipitation, and radiation on climatological time scales due to the advanced physical representation of the underlying processes.