Investigation of Aerosol-Cloud Interactions Using a New Parcel model

It has been increasingly recognized that aerosols can affect climate by indirectly alter cloud microphysical and radiative properties, however, the details of aerosol-cloud interactions remain largely elusive regarding the dispersion effect and separation of aerosol effects from cloud dynamics. This work attempts to address these issues using a new parcel model with detailed bin microphysics. The new model treats coexisting dry aerosols, haze droplets and cloud droplets, and improves consideration of aerosol-cloud continuum. The combined effects of pre-cloud aerosol properties (aerosol concentration, mean radius, aerosol dispersion, and chemical composition) and updraft velocity on cloud microphysical properties (droplet concentration, standard deviation and relative dispersion) are examined by integrating a suite of numerical simulations of different aerosol properties and updraft velocities. The results are further used to extend previous regime classification of aerosol cloud interactions based on effects of cloud droplet concentration (e.g., aerosol-limited vs. updraft-limited regimes) by considering droplet relative dispersion as well. Also examined are the influences of aerosol mean radius, aerosol relative dispersion, and chemical composition on the relationships between aerosol concentration, droplet concentration and droplet relative dispersion. Results from the new model will also be compared with other parcel models in the context of understanding aerosol-cloud interactions and their parameterization in climate models.