Cloud 3D Structure And Radiation (C3SAR) - A joint initiative to account for 3d effects in climate modelling and remote sensing

The cooperative German research unit C3SAR, started in summer 2024, aims at a unique and comprehensive combination of 3D-modelling and observation of clouds and their radiative effects that accounts for the 3D nature of cloud structure The initiative is working towards a physically-based correction of biases in climate modelling and cloud remote sensing, that have been a result from oversimplifications of the complex geometrical and microphysical nature of clouds in previous work.  Along this goal, characteristic 3D cloud structures for relevant cloud regimes from cloud resolving modelling and from synergistic satellite observations will serve as input to radiative transfer modelling of different complexity to quantify the consequences for cloud structure simplifications and to establish physically based cloud-radiation correlations. Long-term high-quality ground-based cloud and radiation observations over Germany provide the validation of these relations by means of radiative closure studies. Current and new generations of satellite sensors such as EarthCARE and Meteosat Third Generation will provide the corresponding closure at the top of the atmosphere. A large field campaign in summer 2026 in Lindenberg, Germany (C3SAR-X), will bring modelling, ground-based and satellite-based remote sensing and in-situ radiation measurements together in a synergetic closure study in order to validate our ability to observe, understand and model the cloud radiative effects and thus to reduce a major source of uncertainty in predicting the future climate. For the second phase of the research unit, it is planned to extend this approach to more globally distributed test-beds in the framework of large international observational networks, to improve the regime-based cloud-radiation relations and apply those to climate modelling and the new generations of satellite sensors. 

We will present methods and concepts of this research unit as well as first results from the initial phase including test case studies and first radiation closure experiments.