Externally Mixed Aerosols to Internally Mixed Aerosols: A Numerical Study of Cloud Processing Using a Bin Aerosol-microphysics Scheme Coupled With WRF

Atmospheric aerosol affects cloud macrophysical and microphysical properties, influences precipitation type and amount, and eventually impacts climate through the interaction between cloud and precipitation. On the other hand, aerosol particles are modulated by cloud and precipitation. Processed by clouds, aerosol particles are redistributed in the air through scavenging (sink) and evaporation (source). Their chemical and hygroscopic features are changed by clouds as well. These redistributed and modified aerosol particles affect radiation, cloud/precipitation and their subsequent development. A new detailed bin warm-phase aerosol-microphysics scheme has been developed to study how aerosol properties such as size, mass and solubility are modified by cloud processing. This scheme simulates the following cloud processes: haze initialization by dry aerosol particles, diffusional growth of haze and cloud drops accounting for both solute and curvature effects, collision-coalescence of cloud drops, Brownian, gravitational, and phoretic collection of haze and dry aerosol particles by cloud drops, sedimentation of dry aerosol particles and rain drops, and wet deposition of aerosol particles by precipitation. By implementing this scheme into the Weather Research and Forecast model (WRF) version 3.2, several sensitivity simulations will be performed by simulating cloud formation over a two-dimensional bell-shaped mountain with periodic lateral boundary condition. How externally mixed aerosols (ex. freshly released black carbon or dust and sulfate) turn into internally mixed aerosols by cloud processing is to be investigated. The properties of aerosols and their effects on radiation, cloud/precipitation and their developments will be examined as well.