Two-way coupling of RACMO2 and LOTOS-EUROS: Implementation of the direct effect of aerosol on radiation

The report describes the extension of RACMO2-LOTOS-EUROS with an explicit treatment of the aerosol direct effect: the impact of aerosol on radiation
through scattering and absorption by aerosol. The extension is meant to replace the existing implementation of the aerosol direct effect in RACMO2 which was adopted from ECMWF IFS Cycle 31 some years ago. That approach was based on combining prescribed fixed spatial patterns of various aerosol species with their associated effective aerosol optical parameters according to the Tegen climatology. However, because it is a climatology, temporal and spatial variations in aerosol optical properties are not captured. A significant improvement is expected when space-time varying aerosol loadings are used. LOTOS-EUROS has a long tradition in aerosol modeling.