Regime Classification and Parameterization of Aerosol-Shallow Cloud Interactions Using Cloud Parcel Models and Observations

It has been increasingly recognized that aerosols can affect climate by indirectly altering cloud microphysical and radiative properties, however, the details of aerosol-cloud interactions remain largely elusive regarding the dispersion effect, separation of aerosol effects from cloud dynamics such as updraft and contribution of entrainments, and regime-dependency. This work attempts to address these issues using cloud parcel models with detailed bin microphysics and observations.

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. Entrainment mixing parameters (entrainment rate, Damkӧhler number and dry air relative humidity) impact on cloud droplet properties as well. Results from both adiabatic parcel model and entrainment parcel model will be compared each other in the context of understanding aerosol-shallow cloud interactions and their parameterization in climate models.