Liquid-Ice Mass Partitioning Across the Edge of Mixed-Phase Cumulus Clouds

One of the major factors controlling the phase partitioning in mixed-phase cloud is entrainment mixing, but it is still poorly understood. In this study, the liquid-ice mass partitioning across the edge of shallow to moderately deep cumulus clouds are analyzed using airborne measurements. The results show the concentration and water content of both liquid and ice decrease toward the cloud edge. However, the liquid mass fraction remains similar across the cloud. The mechanism responsible for the phase partitioning is that extreme inhomogeneous entrainment-mixing dominates. This is evident as both the droplet and ice sizes remain similar with changing concentrations. The comparison between the time scale of turbulent mixing and the phase relaxation time of water also suggests the turbulence strength is too low to homogenize the cloud. The findings from this study improve our understanding on the role of entrainment in phase partitioning, and are useful in evaluating model simulations. In mixed-phase clouds, the coexistence of liquid and ice has significant impacts on the cloud lifecycle and radiative properties, but the phase partitioning in mixed-phase cloud is still not fully understood. In cumulus clouds, one of the major factors controlling the microphysics across cloud edges is the entrainment of dry air into cloud. During the mixing process, the liquid-ice partitioning is determined by the mixing type (homogeneous or inhomogeneous), the evaporation (growth) of liquid, and sublimation (growth) of ice. Currently, there is a lack of observational evidence for the main mixing mechanism that controls the phase partitioning. In this study, the liquid-ice mass partitioning across the edge of shallow to moderately deep cumulus clouds are analyzed using airborne in situ measurements. The results show the liquid mass fraction remains similar across the cloud, and inhomogeneous mixing dominates the phase partitioning. The results improve our understanding on the role of entrainment, and are useful in evaluating model simulations. Liquid-ice mass partitioning across the edges of cumulus clouds is characterized using airborne in situ measurementIn most of the clouds, the liquid and ice water content decrease toward the edge, while liquid mass fraction remains similarThe inhomogeneous mixing dominates the phase partitioning across the cloud edges