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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 14105-14118, 2017
https://doi.org/10.5194/acp-17-14105-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
27 Nov 2017
Partitioning the primary ice formation modes in large eddy simulations of mixed-phase clouds
Luke B. Hande and Corinna Hoose Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
Abstract. State-of-the-art aerosol-dependent parameterisations describing each heterogeneous ice nucleation mode (contact, immersion, and deposition ice nucleation), as well as homogeneous nucleation, were incorporated into a large eddy simulation model. Several cases representing commonly occurring cloud types were simulated in an effort to understand which ice nucleation modes contribute the most to total concentrations of ice crystals. The cases include a completely idealised warm bubble, semi-idealised deep convection, an orographic cloud, and a stratiform case. Despite clear differences in thermodynamic conditions between the cases, the results are remarkably consistent between the different cloud types. In all the investigated cloud types and under normal aerosol conditions, immersion freezing dominates and contact freezing also contributes significantly. At colder temperatures, deposition nucleation plays only a small role, and homogeneous freezing is important. To some extent, the temporal evolution of the cloud determines the dominant freezing mechanism and hence the subsequent microphysical processes. Precipitation is not correlated with any one ice nucleation mode, instead occurring simultaneously when several nucleation modes are active. Furthermore, large variations in the aerosol concentration do affect the dominant ice nucleation mode; however, they have only a minor influence on the precipitation amount.

Citation: Hande, L. B. and Hoose, C.: Partitioning the primary ice formation modes in large eddy simulations of mixed-phase clouds, Atmos. Chem. Phys., 17, 14105-14118, https://doi.org/10.5194/acp-17-14105-2017, 2017.
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Short summary
In this study, the relative contributions of different primary ice nucleation modes (i.e. processes leading to the formation of ice crystals with or without the help of certain aerosol particles, in this case mineral dust) are quantified in model simulations for different cloud types.
In this study, the relative contributions of different primary ice nucleation modes (i.e....
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