On the Scale of Particle Clustering Induced by Inhomogeneous Entrainment‐Mixing in Mixed‐Phase Cumulus Clouds

In mixed‐phase cumulus clouds, droplets and ice crystals are inhomogeneously distributed, such spatial inhomogeneity can be enhanced by inhomogeneous entrainment as it can strengthen the particle clustering, which may further influence the phase partitioning and interactions among hydrometeors. However, the scale of particle clustering induced by inhomogeneous entrainment is not well known. Utilizing high‐resolution in‐situ aircraft measurements in mixed‐phase cumulus clouds, this study shows due to inhomogeneous entrainment‐mixing, the cluster scales of droplets and ice crystals decrease by approximately 10 m from the cloud center to the edge. Changes in the clustering are correlated with the intensity of entrainment‐mixing. Clouds that are significantly affected by entrainment exhibit stronger enhancement of particle clustering and a more noticeable reduction in cluster scale. The findings from this study improve our understanding of the scale of particle clustering induced by entrainment‐mixing, and are potentially helpful in evaluating models. Plain Language Summary Entrainment‐mixing is one of the key processes controlling cloud life cycle and the spatial distribution of hydrometeor. It is known that inhomogeneous entrainment mixing would enhance the clustering of particle distribution in cumulus clouds, but the scales of droplet and ice clusters induced by inhomogeneous entrainment have not been quantified. Utilizing high‐resolution aircraft data sampled in mixed‐phase cumulus clouds, we showed that extreme inhomogeneous entrainment‐mixing fosters pronounced clustering of both droplet and ice particles. Opposite gradients in cluster index and cluster scale from the cloud center to the edge under varying temperature conditions are discovered. On average, the droplet and ice cluster scales decrease by 10 m due to the entrainment. In clouds that undergo intense entrainment, the amplified particle clustering is more discernible and the decrease of cluster scale is markedly greater from the cloud center to the edge. The results enhance the comprehension by quantification of extreme inhomogeneous entrainment‐mixing and are potentially helpful for assessing the performance of model simulations. Key Points The scales of droplet and ice crystal clustering in mixed‐phase cumulus clouds are quantified using airborne in‐situ measurements The inhomogeneous entrainment‐mixing enhances particle clustering near cloud edge, with cluster scales decreasing by 10 m on a