The role of clouds and aerosols in the climate system is still one of the largest uncertainties in the prediction of the future development of climate and in the understanding of the water cycle. Broadening the knowledge about cloud and aerosol processes will not only deepen our understanding of the climate system, but it is an essential prerequisite to assessing the climate effects of transport emissions.
During the last years the Institute of Atmospheric Physics has attained important progress in the airborne and spaceborne remote sensing of aerosols, water, and ice clouds. Passive instruments with high temporal resolution enable to observe the life-cycle of clouds from space. Aerosols and clouds and their respective properties are simulated with global climate models and aerosol-cloud interactions and their role in the climate system are explored. Aerosols modify radiation and clouds, the latter because aerosol particles act as condensation and ice nuclei. A special aerosol module of the climate model simulates the microphysical and chemical properties of the atmospheric aerosol. Current research activities aim at aerosol effects on cirrus clouds and the climate impact of particles from land, sea and air traffic. Comprehensive work also concerns the simulation of cirrus clouds because their complex physics is not yet adequately represented in the climate models so far.
First steps have been carried out to generate realistic virtual satellite images from the results of weather and climate models. These allow not only a direct comparison with real observations, but are also a powerful new method to test cloud parameterizations as well as to develop and verify algorithms for the remote sensing of clouds. The focus in developing novel remote sensing procedures for clouds and aerosols lies on the synergy of active and passive remote sensing by means of lidar, radar, imaging spectrometry, and in-situ methods, this in particular view of the upcoming EarthCARE mission. The combined usage of active and passive sensors allow for a quantitative determination of vertical profiles of cloud properties and their effects on the radiation budget of the Earth from space.
Moreover, we are pursuing an improvement of the representation of the water budget in the upper troposphere in numerical weather prediction and climate models. In particular, we see chances because high performance computers now enable a direct simulation of clouds with ultra-high-resolution models which on the one hand can be validated by observational data and on the other hand can be used as a virtual reality to develop cloud parameterizations.