Microphysical relationships in warm clouds

Relationships among cloud microphysical parameters from six aircraft projec ts carried out over different parts of the globe in different seasons are p resented. Comparisons of project averages showed that projects with higher droplet(2-50 mum diameter) concentrations generally had smaller droplets an d less drizzle (diameter > 50 mum). Hence, when all projects were combined there were negative correlations between droplet concentrations and sizes. However, this was not the case for individual cloud penetrations where only 24% had negative droplet concentration-size correlations. For the stratocu mulus clouds, these negative correlations were more likely to be found in c louds with greater droplet spectral broadening and drizzle. The small cumul us clouds in this study were unique in that 95% of the droplet concentratio n-size correlations were positive regardless of spectral broadening or driz zle. Thus, for the majority of clouds, droplets were smaller in parcels wit h lower droplet concentrations. Entrainment in these clouds was then consis tent with homogeneous mixing that occurs locally and intermittently. The de arth of observations of larger droplets in diluted cloud parcels suggested that mixing of entrained air did not promote droplet growth. (C) 2001 Elsev ier Science B.V. All rights reserved.