Evolution of Cloud Droplet Spectra: The Effect of Nuclei Spectra

Abstract

The particles on which cloud drops nucleate are thought to be of mixed and somewhat variable constitution. Consequently, in the discussion of cloud formation, a number of simplifications and approximations are introduced that can in fact be justified a posteriori. Provided that the spectrum of critical supersaturations of the particles is known (rather than, for example, their size distribution), the resulting theory can be used to predict the concentration of droplets in clouds with errors of order 50%. Thus, the theory can explain, for example, the systematic difference between maritime and continental clouds. Some of the errors may be attributed to sampling problems and some to instrumental problems; a more accurate check on the theory would require the use of improved instrumentation to characterize the aerosol, and the conduct of a cloud-forming experiment under rather well-controlled conditions.