Das Projekt "Europaeisches Wolken- und Strahlungsexperiment: Modellierung, Messungen und Beobachtungen physikalischer Prozesse in Zirruswolken" wird vom Umweltbundesamt gefördert und von GKSS-Forschungszentrum Geesthacht GmbH durchgeführt. High ice clouds, cirrus, tend to enhance the greenhouse effect of the atmosphere while cloud fields tend to decrease it and thus contribute to the cooling of the system. The word is aiming to improve respective algorithms in climate and global/regional circulation models. Extensive airborne and ground-based measurements are performed of microphysical and radiative cloud field properties, and of the dynamical and thermodynamical structure of the ambient atmosphere, where high-resolution satellite imagery provides additional information on the horizontal cloud structure. Campaigns have been made so far over Germany, Scotland and adjacent sea areas, and near Spitsbergen, biggy-packing with other experiments. The work has been concentrating primarily on the high-level ice clouds (cirrus) and lower mostly broken cloud fields. These data are analysed with respect to their relations to larger-scale atmospheric field properties. The case studies will be supported by investigations of detailed processes and their contributions to the observed quantities with cloud resolving numerical models. There are two kinds of models in use: one-dimensional simulating the microphysical properties and the cloud life cycles in response to external forcings (radiation, large scale lifting), and three-dimensional dynamical models to reconstruct observed episodes and estimate future developments. Presently, the model simulations are done without consideration of external atmospheric dynamics (no nesting of cloud models into larger scale models). The spatial resolution ranges from about 100 m to 10 km. Data from Meteosat and the NOAA satellites are analysed with respect to their information contents on cloud properties (ice and water content, particle sizes, radiative transfer properties, and their horizontal structures) for comparison with the field measurements and with the results of the operational ISCCP. Detailed numerical and laboratory studies of scattering and absorption properties of non-spherical cloud particles have been done to improve cloud retrieval algorithms.