PNNL

The Science                                 

Clouds go through three distinct phases during their lives: development, maturation, and dissipation. In this study, researchers conducted large eddy simulations to investigate how cloud shapes, particularly their overall shape and edge irregularities, influence their life cycles. Two new metrics were introduced to quantify cloud shapes—one measuring the overall horizontal shape, and the other assessing the irregularity of the cloud's edge. The study found that while the aspect ratio of clouds remains relatively unchanged, their edges become more irregular over time. This increase in irregularity is strongly linked to the process of cloud splitting, more so than changes in the cloud's aspect ratio. Clouds with more irregular shapes also tend to have smaller gradients in properties at their boundaries, implying enhanced mixing with the cloud-free environment.

The Impact

The findings of this study have significant implications for understanding the evolution of shallow cumulus clouds. The link between the irregularity of cloud edges and life-cycle processes, such as cloud splitting and lateral mixing, sheds new light on the complex interactions between clouds and the atmosphere. Recognizing the impact of cloud shapes and their boundaries on cloud life cycles can lead to more accurate models of cloud behavior, which in turn would enhance weather forecasts and deepen comprehension of climate systems where clouds have been crudely assumed to be circular in the past. This study underscores the importance of accounting for cloud boundary characteristics in cloud physics research.

Summary

This research provides new insights into the life cycle of shallow cumulus clouds by focusing on their shapes and cloud boundary processes. Using large eddy simulations, the study introduces novel metrics to assess cloud shapes and discovers a strong link between edge irregularity and cloud splitting, alongside enhanced mixing with the surrounding environment. These findings highlight the crucial role of cloud edge irregularity in cloud evolution, offering valuable information for meteorologists and climate scientists. The research not only advances understanding of cloud dynamics but also has potential implications for improving weather prediction and climate modeling.

Funding

This study is supported by the Department of Energy, Office of Science, Biological and Environmental Research program as part of the Atmospheric Systems Research program. The modeling studies were supported by the Cascade computational cluster at the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory.