Development of a radiative cloud parameterization scheme of stratocumulus and stratus clouds which includes the impact of cloud condensation nucleus on cloud Albedo

A three-dimensional (3-D) model for simulating the effect of enhanced cloud condensation nucleus (CCN) concentrations on stratocumulus clouds is presented. Results of two-dimensional (2-D) tests are discussed for a control run and a sensitivity run where CCN spectra were taken to be typical of clean marine conditions or mildly continental air, respectively. For a fivefold increase in initial CCN concentrations, drop concentrations increased about threefold, effective radii decreased by 40%, while liquid water contents showed less significant variations. Estimates of effective radius and optical depth from the simulated cloud fields were derived by comparing the 2-D model reflectance functions with the reflectance functions obtained from independent pixel (IP) calculations for a range of effective radii and optical depths. In particular, the maximum differences in the IP-derived versus actual effective radius for the portions of the cloud with an optical depth greater than four ranged from 30% to 50% in both simulations. The domain-mean optical depth was underestimated by nearly 10%, while the maximum differences between the retrieved and actual optical depths were over 20%