Clouds play an important role in the radiation balance of the atmosphere and the climate modifications resulting from human activities. Due to the complexity of the formation processes and the microphysical properties in particular of thin ice clouds their contribution to the greenhouse effect is still not well known. However, it is widely accepted that aerosol particles are very important to initiate the ice formation process.
In the context of several research projects the interaction between aerosols and ice clouds is examined. In the course of field campaigns the characteristics of ice clouds and the physical and chemical nature of the aerosol available in the atmosphere are studied employing the research aircraft Falcon . The project INCA aims at a comparison of the characteristics of cirrus in the clean atmosphere of the southern hemisphere with those in the polluted northern hemisphere. An estimate of the effects of human activities on the climate via the modification of the cloud characteristics is expected. In the project PAZI the properties of very thin ice clouds are examined.
For these tasks an extensive equipment for aerosol measurement was set up at the institute. In laboratory studies and process models the interaction between aerosols and ice crystals is examined for well defined particles and in model systems. In connection with the observations under real conditions an improved representation of cloud formation processes in climate models is expected which is an important issue for a more realistic prediction of expected climate changes. Particles emitted from aircraft at cruise are released into the atmosphere at altitudes where ice clouds form. In the project PartEmis particles emitted from aircraft engines are characterised in detail regarding their physical and chemical properties and their ability to initiate cloud droplet formation. Building on earlier research work at the institute on the direct emissions of air traffic the current activities aim at a better understanding of the influence of air traffic on the atmosphere and the climate.