Dependence of entrainment on vertical velocity and distance to cloud edge

The dependence of entrainment rate on environmental conditions and cloud characteristics is investigated using large-eddy simulations (LES) of the response of shallow cumulus convection to a small-amplitude temperature perturbation that is horizontally uniform and localized in height. The simulation results are analyzed in the framework of an ensemble of entraining plumes by tracking a large number of Lagrangian parcels embedded in the LES. The results show that fractional entrainment rate of a plume is inversely proportional to its vertical velocity and its distance to the cloud edge, while changes in environmental stratification and relative humidity, the plume's buoyancy, or the vertical gradient of its buoyancy due to the temperature perturbation have little effect on the entrainment rate.