Aerosol Impacts in Shallow Convection as Simulated by Bin and Bulk Microphysical Schemes in RAMS

The indirect effects of aerosols on cloud systems continues to be an area of active research. One reason for the uncertainty in cloud response to changes in aerosol concentrations is that our microphysical parameterizations must make assumptions about cloud properties that may not always be appropriate. Bin microphysical schemes are generally considered more realistic than bulk schemes since they allow for a better representation and evolution of cloud species. The spectral bin model (SBM) developed at the Hebrew University has been coupled to the Regional Atmospheric Modeling System (RAMS). RAMS also has an advanced, bin-emulating, two-moment bulk microphysical scheme. This setup provides a unique opportunity to compare results of the bin-emulating scheme with the SBM under the same dynamical framework. Simulations of shallow cumuli have been performed using each scheme with initial aerosol concentrations representative of clean and dirty marine environments. The resulting differences in cloud properties and precipitation will be examined for each scheme with a focus on the role of entrainment. Furthermore, the reasons for different sensitivities of shallow cumuli to aerosol concentration between the two schemes will be linked back to the parameterizations themselves.