Aerosols and cloud droplets in the atmosphere appear in different sizes. They can be transported by wind and experience various microphysical changes due to nucleation, collisional and condensational growth, evaporation and sedimentation. These microphysical processes affect optical properties of clouds and aerosols, and through it, they affect climate. Climate models usually lack a microphysical module, but instead use various parameterizations to represent clouds in the terrestrial atmosphere. Coupling between cloud microphysical models and climate models could improve the quality of numerical predictions of climate. In this study, CARMA (Community Aerosol and Radiation Model for Atmospheres), which is one of the best available microphysical models for calculation of size distributions of atmospheric aerosols and cloud droplets based on environmental conditions, has been redesigned and rewritten for coupling with numerical models of climate. In the revised model, data transfer between subroutines is handled via lists of arguments. The microphysical part of CARMA v. 2.2 was isolated from other processes, such as radiation and transport, and prepared for coupling with existing climate models. Changes were made to the vertical transport subroutines. The PPM (Piecewise Parabolic Method) method of solving the advection equation was replaced with the REA (Reconstruct-Evolve-Average) method, complemented with the minmod slope limiter. The sedimentation equation is now solved using the upwind method. Sedimentation fluxes, used by the upwind method, are calculated inside the microphysical part of CARMA. The ability of the revised CARMA model to reproduce the observed microstructure of a marine stratocumulus cloud over the North Sea was tested. The improved model closely reproduces most of the observed properties of the cloud and aerosols.M.S.Includes bibliographical references (p. 102-104)
