Parameterization of Compensating Aerosol-Cloud Interaction Factors for Climate Models

Despite progress in understanding of aerosol-cloud interactions and their representation in climate models, climate models still suffer from a large uncertainty in estimated aerosol indirect effects and a large discrepancy compared to observations. It has been increasingly recognized that part of these vexing problems is likely due to largely overlooked factors that work to compensate the traditional aerosol effect through affecting droplet concentration, e.g., 1) non-monotonic changes of cloud properties with increasing aerosol concentration, 2) dispersion effect associated with changes in the spectral shape of the cloud droplet size distribution, and 3) effect of entrainment-mixing processes. This study will report our research on these poorly understood compensating factors, with an emphasis on their relationships to the traditional understanding and how to parameterize these factors in climate models. The research is based on a combined investigation of observational analysis, numerical modeling and theoretical formulation.