Ice multiplication in simulated deep convective clouds with the ICON model

Ice multiplication processes have been recognized to play an important role in the forming of cloud ice crystals, and multiple mechanisms have been proposed to describe ice multiplication. Ice multiplication processes have been investigated for a variety of cloud types, but mostly for stratiform clouds or shallow cumulus, which do not reach temperatures of homogeneous freezing. In this study, sensitivity experiments are performed to study the role of ice multiplication in the developing stages of deep convective clouds. A double-moment cloud physics scheme was adopted. Except as the default Hallett-Mossop rime splintering process, two additional ice multiplication processes, which are droplet shattering during the freezing of supercooled drops and the collisional breakup of ice particles, are implemented. Moreover, two different parameterization schemes for the collisional breakup of ice particles. Simulation results reveal that the ice multiplication processes have a significant impact on the cloud microphysical properties and thermodynamic phase distribution within the cloud. At the cloud top, the fingerprint of ice multiplication is weaker. Collisional breakup is found to dominate ice multiplication, and the collisional breakup process rate is larger than rime splintering and droplet shattering process rates by 4 and 3 orders of magnitude, respectively. The ice enhancement factor (the ratio of ice mass or number in simulations with and without ice multiplication) has a strong vertical variation, with the maximum around -10°C and -25°C. Besides, the cascade effect on ice cloud number concentration was also investigated.