There is strong observational evidence, supported by model results, suggesting that entrainment occurs at the top of ascending turrets. However, we still do not have a clear picture of how the entrained air is mixed into the body of the cloud. Laboratory studies and observations in the field suggest that the air is swept around the side of the ascending thermal to enter through the rear.

As part of a study into whether the cloud droplet size distribution can be explained by supersaturation variations along trajectories, we have examined the dynamical structure of small, warm clouds and, in particular, the relative importance of shear and mixing at the cloud edges. Observations of the thermal structure and the sharpness of cloud edges made in small cumulus clouds during the Small Cumulus Microphysics Study in Florida will be compared with model results. We will present results from preliminary analysis of the air flow, the relationship between the characteristics of thermals and the environment (such as stability and wind shear), the size and persistence of adiabatic regions, and the relative magnitudes of the processes strengthening and weakening the gradients at cloud edge.