Aerosol effect on the mobility of cloud droplets

Cloud droplet mobility is referred to here as a measure of the droplets' ability to move with ambient air. We claim that an important part of the aerosol effect on convective clouds is driven by changes in droplet mobility. We show that the mass-weighted average droplet terminal velocity, defined here as the `effective terminal velocity' (eta) and its spread (sigma eta) serve as direct measures of this effect. Moreover, we develop analytical estimations for eta and sigma eta to show that changes in the relative dispersion of eta (epsilon eta = sigma eta/eta) can serve as a sensitive predictor of the onset of droplet-collection processes.