Does Entrainment at Edges of Cumulus Clouds Produce Broader Droplet Size Distributions Compared to in the Unmixed Cloud Interior? An In-Situ Airborne Study

We explore the effect of cumulus entrainment on droplet size distributions using in-situ aircraft data collected in growing cumulus during the SPICULE field project carried out over the central US. Droplet sizes at the cloud edges are compared with the relatively unmixed interior of the cloud. Droplets with diameters larger than 10 µm are measured using the holographic detector for clouds, HOLODEC-II. Conservation of moist static energy is used to evaluate the degree to which interior regions are unmixed, and edge regions are selected just outside the interior at the same height above cloud base. Unmixed cloud interiors and cloud edges are compared at multiple heights above cloud base and for clouds with various temperature profiles. This analysis can help identify conditions where entrainment influences cloud droplet sizes, revealing the physical mechanisms which may be involved. We aim to assess whether or not broadening of droplet size distributions occurs at cloud edges, which is relevant to collision-coalescence and subsequent growth of large cloud droplets.