The current state of knowledge of the Venusian clouds is reviewed. The visible clouds of Venus are shown to be quite similar to low level terrestrial hazes of strong anthropogenic influence. Possible nucleation and particle growth mechanisms are presented. The Pioneer Venus experiments that emphasize cloud measurements are described and their expected findings are discussed in detail. The results of these experiments should define the cloud particle composition, microphysics, thermal and radiative heat budget, rough dynamical features and horizontal and vertical variations in these and other parameters. This information should be sufficient to initialize cloud models which can be used to explain the cloud formation, decay, and particle life cycle.
Knollenberg, R G;  Hansen, J;  Ragent, B;  Martonchik, J;  Tomasko, M 
- Particle Measuring Systems, Inc., 1855 South 57th Court, Boulder, Colorado 80301, U.S.A.
- National Aeronautics and Space Administration, New York (USA). Goddard Inst. for Space Studies
- National Aeronautics and Space Administration, Moffett Field, Calif. (USA). Ames Research Center
- Jet Propulsion Lab., Pasadena, Calif. (USA)
- Arizona Univ., Tucson (USA)