The importance of ice nucleating particle types and modes for the initiation of the ice phase and precipitation: Model simulations based on laboratory measurements.

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In this project model simulations will be performed with COSMO-SPECS, a 3D cloud model which includes a spectral bin microphysical scheme for aerosol particles and hydrometeors. As the microphysics package is the same contained in the air parcel model used during INUIT-1, all new developments and modifications from INUIT-1 will be transferred into COSMO-SPECS. First an artificial test case, i.e. a heat bubble over a flat terrain, will be simulated and sensitivity studies will show the development of the ice phase and precipitation under realistic variations of ice nucleating particle types and distributions. Another focus of the sensitivity studies will lie on the effects of so-called small triggers, i.e. ice nucleating particle types (e.g., biological particles) or freezing modes (such as contact freezing) which do not show significant effects on the first sight but might influence the dynamics of the cloud in the way that in the end ice formation is enhanced. Finally a real case study based on INUIT field experiments will be performed in joint cooperation with RP5. The contributions of the different ice forming modes will be quantified and, thus, the atmospheric relevance of the ice nucleation regimes which are investigated in INUIT laboratory and field projects will be estimated. Simultaneously, parameterizations of new particle types studied during INUIT-2 will be developed and included into the microphysical scheme. Existing parameterizations will continuously be modified and improved. As part of the project a number of laboratory experiments will be performed to investigate contact and immersion freezing by means of the Mainz vertical wind tunnel and an acoustic drop levitator. Here the focus lies on the improvement of contact freezing experiments. They will be conducted at the Mainz vertical wind tunnel with supercooled drops freely floated in an air stream which carries the potential contact ice nucleating particles along with. Thus, the number of collisions between drops and particles can be calculated and the freezing efficiency, i.e. the freezing probability for one drop-particle collision can be determined.