ABSTRACT

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.