Bin Microphysics for Improving Boundary Layer Clouds

Abstract:

Boundary layer clouds strongly control the planetary albedo. In the Community Earth System Model, a two moment bulk microphysics parameterization cooperates with a subgrid-scale turbulence parameterization to simulate boundary layer clouds. We substitute the Morrison Gettelman (MG) microphysics parameterization with the bin microphysics Community Aerosol and Radiation Model for Atmospheres (CARMA). The obsMIPs datasets of cloud fraction, specific humidity, and precipitation guide our model development. Lifetime, albedo, and precipitation are sensitive to the microphysics parameterization. Precipitation in CARMA is a direct integration of the coalesence and sedimentation equations using CARMA's predicted size distribution. In contrast, MG parameterizes autoconversion and accretion as a fixed function of cloud water and droplet number based on an external model.