Modeling in AMP
CAM version 5 (CAM5) has been modified substantially with a range of enhancements and improvement in the representation of physical processes since version 4 (CAM4).
A new moist turbulence scheme explicitly simulates stratus-radiation-turbulence interactions, making it possible to simulate full aerosol indirect effects within stratus. A new shallow convection scheme uses a realistic plume dilution equation and closure that accurately simulates the spatial distribution of shallow convective activity. Computation of an updraft vertical velocity now allows for aerosol-cumulus interactions. The revised cloud macrophysics scheme provides a more transparent treatment of cloud processes and imposes full consistency between cloud fraction and cloud condensate. Stratiform microphysical processes are represented by a prognostic, two-moment formulation for cloud droplet and cloud ice, and liquid mass and number concentrations. The scheme allows ice supersaturation and features activation of aerosols to form cloud drops and ice crystals. The radiation scheme has been updated to the Rapid Radiative Transfer Method for GCMs (RRTMG) and employs an efficient and accurate correlated-k method for calculating radiative fluxes and heating rates. RRTMG has an extensive spectral representation of the water vapor continuum and offline agreement with line-by-line calculations is significantly improved. The 3-mode modal aerosol scheme (MAM3) has been implemented and provides internally mixed representations of number concentrations and mass for Aitkin, accumulation and course aerosol modes.
A full inventory of observationally based aerosol emission mass and size is provided in standard available datasets. These major physics enhancements permit new research capability for assessing the impact of aerosol on cloud properties. In particular, they provide a physically based estimate of the impact of anthropogenic aerosol emissions on the radiative forcing of climate by clouds.