Atmospheric aerosols exert important “indirect effects” on clouds and climate by serving as cloud condensation nuclei (CCN) and ice nuclei that affect cloud radiative and microphysical properties. For example, an increase in CCN increases the number concentration of droplets enhances cloud albedo, and suppresses precipitation that alters cloud coverage and lifetime. However, in the case of moist and strong convective clouds, increasing aerosols may increase precipitation and enhance storm development. Although aerosol-induced indirect effects on climate are believed to have a significant impact on global climate change, estimating their impact continues to be one of the most uncertain climate forcings.
BNL tackles the interwoven issues using a blend of theory, observations (in situ and remote sensing), and modeling. We focus on improving the parameterizations of aerosol properties and cloud microphysics that are critical for evaluating indirect aerosol effects, such as parameterizations of aerosol hygroscopicity, CCN spectrum, droplet activation, number concentration, and the autoconversion process. This comprehensive, multi-faceted approach enables addressing important issues over a wide range of scales (from cloud-scale to climate model grid scale). Newly developed parameterizations and/or physical understanding are evaluated using a suite of modeling tools as part of the FASTER project.