Application of a new parametrization framework for heterogeneous ice nucleation in a regional- scale model

Romy Ullrich, C Hoose, B Vogel, H Vogel, D Rieger, K Deetz, D Cziczo, K Froyd, J Schwarz, O Moehler

In cirrus clouds ice can be formed by both homogeneous and heterogeneous ice nucleation. In models the competition between homogeneous and heterogeneous ice nucleation is parameterized depending on the updraft velocity and aerosol concentration (Barahona and Nenes, 2009; Kaercher et al., 2006). Both influence the maximum ice saturation ratio. Because heterogeneous ice nucleation occurs for lower ice saturation ratios compared to homogeneous ice nucleation, an increase in aerosol particle concentration will result in more heterogeneously formed ice and therewith an earlier depletion of water vapor. The resulting ice saturation ratio may be decreased in such a way that homogeneous ice nucleation is inhibited (DeMott et al., 2003). Therefore, the efficiency of aerosol particles to form ice crystals has to be well known in order to simulate the cloud formation in this competition framework.

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