Maritime–Continental Drizzle Contrasts in Small Cumuli

Abstract

Continuous aircraft measurements of cloud condensation nuclei (CCN) were made during 16 summertime flights in eastern Florida. The air masses were divisible into maritime and continental regimes that respectively corresponded to wind direction-easterly (onshore) and westerly (offshore). Throughout these small cumulus clouds there were consistently higher concentrations of smaller droplets in the continental air. There was much more drizzle (diameter 50 m) in the maritime clouds where drizzle was associated with larger mean cloud droplet (2-50-m diameter) sizes, higher concentrations of large cloud droplets, and greater amounts of cloud droplet liquid water. An apparent cloud droplet mean size threshold for the onset of drizzle was almost never exceeded in the continental clouds but was often exceeded in the maritime clouds, especially at higher altitudes. All together these results demonstrate that higher CCN concentrations suppressed drizzle.