Distinct Mixing Regimes in Shallow Cumulus Clouds

Understanding the nature of mixing between cloudy air and its surroundings is an important and yet, open question. In this research, we use high-resolution (10 m) bin-microphysics Large Eddy Simulation of a cumulus cloud, together with a Lagrangian passive tracer tracking method, to study mixing. We analyze the passive tracers as a function of their trajectories and the thermodynamic conditions they undergo inside and outside the cloud. Three main mixing regimes (core, periphery, and skin) are identified, each determining a subset of tracers with similar trajectories. These mixing regimes can be observed throughout the cloud's lifetime and they provide evidence for the presence of an undiluted core in shallow cumulus clouds. At the dissipation stage, a fourth regime is identified: cloud-top entrainment followed by downdrafts. The mixing of shallow clouds with their environment is a key open question in climate research and prediction. This topic is challenging due to the complexity of cloud processes and the difficulty of accurately measuring and modeling them. This study uses high-resolution simulation and Lagrangian tracers to analyze mixing. The study identifies three different mixing regimes in cumulus clouds throughout their lifetime. Each regime is characterized by specific types of tracer trajectories. A fourth regime is identified as part of the clouds' decay. Three mixing regimes are identified using subsets of tracers with similar trajectories in the Large Eddy Simulation of a cumulus cloudThese mixing regimes persist throughout the cloud's lifetime, providing insights into cloud mixing dynamicsThe dissipation stage of the cloud reveals cloud-top entrainment followed by downdrafts