A Sectional Cloud Microphysical Model (CARMA Cloud) in the Community Earth System Model (CESM2)

Clouds are critical to global radiative forcing and the climate system of Earth. However, cloud simulations in climate models remain highly uncertain. The current cloud model in the Community Earth System Model (CESM2/CAM6) separates cloud-size particles from raindrops and snow and uses bulk microphysics. Here, we develop a sectional cloud model that unites the liquid cloud-size particles with rain and ice cloud-size particles with snow within single size distributions in the Community Aerosol and Radiation Model for Atmospheres (CESM2/CARMA Cloud). Graupel is included in the model, but not currently active. The CARMA cloud model better represents the microphysical processes of clouds in the climate model, but at added computational cost. We will describe the performance and evaluation of the CESM2/CARMA cloud model. Simulated cloud properties including cloud fraction, liquid and ice water path, and effective radius will be compared to data. Cloud radiative forcing will be evaluated using data from the Clouds and the Earth’s Radiant Energy System (CERES). A long-term free-run will be used to evaluate the performance of this model in climate projections.