AbstractThermodynamic analysis of aircraft observations of the downdraughts at the edges of small maritime cumulus clouds is used to obtain estimates of the rate of entrainment of cloudy air into the downdraughts. The entrainment rates are around 10−4to 10−2s−1. A simple entraining parcel model is used to investigate the fate of droplets entrained at this rate into such downdraughts. It is shown that the majority of small droplets evaporate totally, resulting in a subsaturation in the downdraught of less than 1%, except close to cloud top or cloud base. However, a few droplets which contain large soluble nuclei continue to grow, or undergo only a small amount of evaporation, during their descent. The limited evaporation ensures that some droplets undergoing a cycle of ascent and descent will grow even without net ascent. The largest droplets at some levels are therefore to be found in the downdraughts although the droplet concentration and liquid water content are much lower than in the cloud at the same level. The calculated growth and the thermodynamic properties of the downdraughts are in good agreement with observations of small maritime cu