In larger-scale atmospheric chemistry models, clouds are found to strongly influence photolysis rates, and precipitation from clouds is an important process removing reactive atmospheric constituents. Both of these effects are largely parameterized and highly simplified since individual clouds cannot be adequately resolved in current atmospheric models. However, a key assumption which must be made in order to adequately account for clouds is not only their spatial and temporal distribution, but their OVERLAP. In this paper, several simplified calculations are performed using a typical cloud parameterization which shows that cloud overlap assumptions strongly influence radiation and scavenging calculations. A wide range of calculated photolysis rates or scavenging rates can be obtained by relatively minor adjustments in the assumed vertical overlap distribution of particular cloudy environments. These results suggest that most cloud parameterizations would inherently contain an almost unacceptable level of uncertainty that influences nearly all subsequent model calculations
Symposium on Interdisciplinary Issues in Atmospheric Chemistry