Examination of CCN impacts on hail in a simulated supercell storm with triple-moment hail bulk microphysics

Aerosols that act as cloud condensation nuclei (CCN) play a crucial role in the formation of cloud particles and recent research suggests that CCN can influence ice processes within deep convection as well. In this study, a triple-moment bulk hail microphysics scheme is used to investigate the impact of changing CCN concentrations on hail for a well-observed supercell storm that occurred over northwest Kansas on 29 June 2000 during the Severe Thunderstorm and Electrification and Precipitation Study (STEPS). For the simulated supercells in the particular environment examined, an increase in potential CCN concentrations from 100 to 3000 cm− 3 leads to increasing numbers and decreasing sizes of cloud droplets, as expected, yet the overall storm dynamics and evolution are largely unaffected. Increases in potential CCN concentrations lead to non-monotonic responses in the bulk characteristics of nearly all hydrometeor fields, surface precipitation, and cold-pool strength. However, higher concentrations of CCN also result in larger hail sizes and greater amounts of large diameter (≥ 2 cm) hail. The results suggest that a combination of increased sizes and localized reductions in numbers of hail embryos near favorable growth regions with increasing potential CCN concentrations tend to promote conditions that lead to increased hail sizes and amounts of large hail.