Aerosol-Cloud-Precipitation Interactions in the Climate System
Prof. Dr. Meinrat Andreae (Max-Planck-Institut für Chemie Mainz)

Aerosols serve as cloud condensation nuclei (CCN) and thus have a substantial effect on cloud properties. Increased aerosol concentrations resulting from anthropogenic pollution lead to higher cloud droplet concentrations, but smaller droplet sizes. This in turn affects the physical processes inside clouds that lead to the initiation of precipitation. Depending on a number of factors, including aerosol composition, atmospheric stability and cloud water content, increasing CCN concentrations may either decrease or increase rainfall. In convective clouds, early rain formation is suppressed, which makes more water and energy available to rise higher in the atmosphere and form ice particles. This may invigorate the dynamics of convection, encourage the formation of hail and lightning, and enhance the transport of materials to the upper troposphere. I will present recent advances in the conceptual understanding of aerosol-precipitation interactions, and highlight requirements to include these interactions in climate models.