AbstractThe formation of buoyancy reversal due to entrainment of dry environmental air, and its implication for cumulus dynamics, are discusses. Concepts originating from laboratory experiments with reacting turbulent flows, and from numerical simulations of homogeneous and isotropic turbulence, are applied to distinguish between large‐scale entraining eddies developing at the interface, subsequent development of smaller‐scale motions, and final homogenization by microscale processes. The physics of the microscale homogenization by molecular diffusion and sedimentation of cloud droplets is discussed. It is shown that, as a result of droplet sedimentation, much smaller negative buoyancy (buoyancy undershoots) may be generated on cloud microscale as compared with the value predicted by a classical nonlinear mixing diagram of cloudy and cloud‐free air.Highly idealized numerical experiments aimed at simulating the temporal evolution of a small convective cloud were performed with and without the effects of molecular mixing that results in buoyancy reversal. It is argued that these experiments provide two limiting cases, and that the dynamics of a real cumulus cloud is located somewhere between them. The major effect of buoyancy reversal as suggested by these experiments is to increase the intermittency associated with cloud evolution. The temporal variation of cloud‐top height, maximum undraughts, and minimum downdraughts increases significantly when buoyancy reversal is allowed.It is argued that results of numerical experiments, together with other laboratory and theoretical studies, cast serious doubts on the concept of cumulus entrainment being driven by the cloud‐top entrainment instability.