middle picture: cloud laboratory (© of the picture: Stefan Müller-Naumann)

The activation of cloud droplets, i.e., the formation of cloud droplets on aerosol particles present in the atmosphere, is one oft he most important atmospheric aerosol cloud interaction processes. Aerosol particles that can be activated to cloud droplets are called Cloud Condensation Nuclei (CCN). Without these CCN there would be no clouds and also no precipitation. Therefore the number, the size, and the chemical composition of atmospheric aerosol particles may significantly influence the properties of clouds and affect both weather and climate. Consequently it is important to understand and quantify, how aerosol particles influence the activation of cloud droplets and clouds themselves. Goals of the investigations performed at TROPOS concerning this topic are:

  • improve understanding with respect to the important parameters and properties controlling the activation behavior of cloud droplets  
  • quantification and compilation of climatologies of atmospheric CCN properties

Investigations concerning the activation of cloud droplets comprise both, consideration of activation processes in real clouds, and the simulation of activation processes under well-controlled laboratory conditions.