Ice crystals play an important role for the radiative properties of clouds as well as for the formation of precipitation. Mixed-phase clouds are clouds that consist of both, super-cooled liquid droplets and ice particles. They account for a large fraction of the clouds in the atmosphere but our knowledge on the microphysical properties of these clouds is still limited. An important question is how ice forms in these clouds. While it is well established that an ice nucleus is needed as a seed for the initial formation of an ice crystal in mixed-phase clouds many questions remain to be answered on the concentration and variability of atmospheric ice nuclei and their physico-chemical properties.

The Research Unit “INUIT” (Ice Nuclei research UnIT) studies heterogeneous ice formation in the atmosphere. The studies include laboratory investigations on the nature of the nucleation process and on the chemical, microphysical and biological characterization of atmospherically relevant ice nuclei as a function of temperature and water saturation. Intensive field experiments are conducted as well as monitoring surveys to study the number concentration, variability, size, chemical composition, surface properties and sources of atmospheric ice nuclei in different freezing modes. Various state-of-the-art methods and facilities are used for the characterization of the ice nuclei. Ice nucleating properties of mineral dust particles, volcanic ash, and biological ice nuclei are a focus of attention of the INUIT research unit. The results of the experimental investigations are fed into a cloud process model and a cloud-resolving meso-scale model to improve the representation of clouds in the models, to simulate cloud processes and to quantify the contribution of ice nuclei types and freezing modes.

The INUIT research unit comprises 9 research projects from 8 partner institutes (Goethe-University of Frankfurt/Main, University of Bielefeld, University of Mainz, Technical University Darmstadt, Leibniz-Institute for Tropospheric Research, Max-Planck Institute for Chemistry and Karlsruhe Institute for Technology). It is funded by the Deutsche Forschungsgemeinschaft DFG (grant no. FOR 1525).