The Effects of Shallow Cumulus Cloud Shape on Interactions among Clouds and Mixing with Near‐Cloud Environments

Cloud lifecycles are influenced by interactions among clouds and mixing with cloud-free environments. Cloud shapes dictate the length of cloud boundaries, which affects these interactions. This study uses a large eddy simulation to examine the relationships between the shallow cumulus cloud shapes, processes at their boundaries, and lifecycles. To characterize the shape of clouds, two metrics are newly defined: one reflects the overall horizontal cloud shape, and the other defines the cloud edge irregularity. Simulated clouds experience increased irregularity, but little changes in aspect ratio. Irregularity-driven cloud perimeter growth strongly indicates cloud splitting, with a more pronounced effect than aspect ratio-driven perimeter growth. Smaller cloud-shell gradients of properties across cloud boundaries are associated with more irregular clouds, suggesting enhanced mixing of clouds with the cloud-free environment. These findings indicate that the shallow cumulus evolution is partly driven by the irregularity of the cloud edge through lateral mixing and cloud splitting. This study uses computer simulations of small fluffy clouds to examine how the shape of these clouds impacts their evolution. As clouds evolve, their edges become more jagged, but their overall shape does not change much. Clouds with more jagged edges are more likely to split in two. Furthermore, the jaggedness of the cloud edge affects mixing with the surrounding clear air, which influences cloud growth and decay. These findings highlight the importance of irregularity on the edge of the cloud for the evolution of entire clouds. Shallow cumulus clouds develop more irregular edges while maintaining a similar overall shape as they ageThere is more perimeter growth before clouds split than merge, led by more irregular edges than by changes in overall shapeThe growth of the cloud perimeter led by irregular edges relates to small differences with nearby clear air attributed to lateral mixing