A new physically-based parameterization of ice cloud formation for large-scale simulations

This study presents a comprehensive ice cloud formation parameterization framework that computes the ice crystal number, size distribution, and maximum supersaturation from precursor aerosol and ice nuclei with any size distribution and chemical composition. The parameterization provides an analytical solution of the cloud parcel model equations and accounts for the competition effects between homogeneous and heterogeneous freezing, and, between heterogeneous freezing in different modes. The diversity of heterogeneous nuclei is described through a nucleation spectrum function that depends on the surface area, chemical composition, and size distribution of the precursor, insoluble aerosol. The parameterization reproduced the predictions of a detailed numerical parcel model. The average error in ice crystals number concentration was -2.0 ± 8.5% for conditions of pure heterogeneous freezing, and, 4.7 ± 21% when both homogeneous and heterogeneous freezing were active. Apart from its rigor, excellent performance and versatility, the formulation is extremely fast and free from requirements of numerical integration.