FOR 1525: INUIT - Ice Nuclei Research Unit

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Ice crystals in the atmosphere play an important role for the formation of precipitation and for the radiative properties of clouds. 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 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 characterisation 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 characterisation of the ice nuclei. Ice nucleating properties of mineral dust particles, volcanic ash and biological ice nuclei are a focus of attention within the Research Unit. The results of the experimental investigations are fed into a cloud process model and a cloud-resolving mesoscale 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.