Clouds in the next generation of the Community Earth System Model

Abstract:

Cloud processes are critical uncertainties in Earth System Models. Simulated clouds also have significant biases with respect to observations. This presentation will describe updated cloud parameterizations in the next generation of the Community Atmosphere Model being finalized for release in 2016. New CESM cloud formulations will be described, as well as some of the methodologies for how and why the model was altered. Major improvements include a more unified treatment of sub-grid variability and moist turbulence, improvements in cloud microphysics and aerosols and the coupling between different cloud processes. Methodologies for evaluation used included detailed comparisons to observations, forecast experiments, constrained hindmost experiments and objective parameter optimization experiments. These methods will be described. The new model has significant reduction in some long standing cloud biases, such as reductions in excessive shortwave absorption over the S. Ocean. Evaluation of the model state and its representations of aerosol-cloud interactions and cloud feedbacks will be discussed.