Physical-Chemical Processes of Cloud Activation studied with a Desktop Cloud Model Schwartz S. E. 6th International Conference on Air-Surface Exchange of Gases and Particles, Edinburgh, July 3-7, 2000.

A model of the activation process of a zero-dimensional cloud is described. The model runs in Mathematica, a platform-independent environment for numerical computation. Key input parameters are updraft velocity and the dry distribution of number and composition of aerosol particles; 25 bins in the dry radius range 9 to 280 nm provide an accurate representation of microphysical dynamics. As the parcel is cooled water vapor is taken up by aerosol particles, governed by the difference between the ambient water vapor partial pressure and the equilibrium partial pressure above each drop, as given by the Kšhler expression. As environmental supersaturation increases, initially larger particles, and then successively smaller particles may activate. The environmental supersaturation reaches a maximum and then decreases, effectively limiting the radius range of activated particles. This "desktop cloud" can be used to explore a variety of phenomena: the dependence of maximum supersaturation on environmental variables such as updraft velocity, aerosol properties and the presence of soluble and/or reactive gases; to examine the locus of uptake and aqueous-phase reaction of gases and the resultant influence on the particle size distribution; and to test parametrizations of aerosol influences on cloud microphysics.


This page was last updated 2000-09-27.

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