The Graduate Center for Cloud Physics Research at UMR has developed a cloud simulation facility to study phenomena occurring in terrestrial clouds and fogs. The facility consists of a pair of precision cooled-wall expansion chambers along with extensive supporting equipment. The smaller of these chambers, described in this article, is fully operational, and is capable of simulating a broad range of in-cloud thermodynamic conditions. It is currently being used to study water drop growth and evaporation for drops nucleated (activated) on well-characterized aerosol particles. Measurements have been made not only for continuous expansions (simulated updraft) but also for cyclic conditions, i.e., sequences of expansion-compression cycles resulting in alternating drop growth and evaporation. The larger of the two cloud chambers is nearing completion and will provide a broader range of conditions than the smaller chamber. The facility is supported by a fully implemented aerosol laboratory which routinely produces well-characterized condensation nuclei. The aerosol laboratory contains extensive instrumentation designed to both shape and measure the size distribution and nucleating characteristics of the generated aerosol. The cloud simulation facility also includes a humidifier to bring an air sample to a known humidity before it is put into the cloud chamber. A systematic program to infer effective condensation coefficients (of water vapor on cloud drop) under a variety of well-controlled simulated in-cloud conditions is now under way. Analysis of current experiments with standard drop growth theory indicates a variation of condensation coefficient with observation time, with values sufficiently low to explain one of the current mysteries in cloud physics: viz., the broad spread of drop sizes observed in natural clouds. This article includes a description and performance specifications of the smaller cloud simulation chamber.



Second Department

Mechanical and Aerospace Engineering

Third Department


International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version

Final Version

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© 1987 American Institute of Physics (AIP), All rights reserved.

Publication Date

01 May 1987