The impact of the physico-chemical microstructure of atmospheric aerosols on the formation of stratiform clouds

A one-dimensional model of the cloud topped planetary boundary layer is presented. Special emphasis is layed on a detailed description of cloud microphysical processes. Aerosols and cloud dropletes are treated in a joint twodimensional particle distribution whereby the activation of aerosols is explicitely calculated by solving the droplet growth equation at all relative humidities. Numerical results are presented for three different types of aerosol particles: urban, rural and maritime. It is shown that the life cycle of stratiform clouds is strongly controlled by the physico-chemical microstructure of the atmospheric aerosols. This holds in particular for the cloud water content, the form of the microphysical droplet size distribution and the vertical extent of the cloud. It is concluded that besides the direct influence of atmospheric aerosols on the global climate the indirect impact via different cloud formation is an important issue and should therefore be accounted for in climate models.