Improved Simulation of Arctic Clouds in the Community Atmosphere Model
Arctic clouds are a major controller of the surface net radiative budget, and it is important that climate models produce these clouds correctly to accurately represent Arctic climate. The Arctic Ocean’s surface alters between ocean and sea ice. This variation, along with atmospheric dynamics and thermodynamics, affects Arctic cloud properties. U.S. Department of Energy (DOE) scientists at Lawrence Livermore National Laboratory (LLNL) developed a method to evaluate Arctic clouds in the Community Earth System Model’s (CESM) two most recent global atmospheric models that are used in the coupled transient climate projections, the Community Atmospheric Model Version 4 and 5 (CAM4 and CAM5). Clouds were first examined during distinctly separate dynamical and thermo-dynamical conditions, which were called synoptic regimes. Next, cloud fractions for each regime were examined when the regime occurred over open-ocean, sea ice, and land. The scientists ran CAM4 and CAM5 using the DOE Cloud-Associated Parameterizations Testbed (CAPT) framework to ensure the dynamics and thermodynamics in the models were similar to the observations. From CAM4 to CAM5, there was a large community effort to improve the representation of boundary layer clouds, which are prevalent in the Arctic. This analysis demonstrated that the new boundary layer turbulence and cloud microphysical schemes in CAM5 produced a global atmospheric model with improved Arctic cloud sensitivity to lower tropospheric stability and Arctic surface type.
Barton, N. P., S. A. Klein, J. S. Boyle, and Y. Y. Zhang. 2012. “Arctic Synoptic Regimes: Comparing Domain-Wide Arctic Cloud Observations with CAM4 and CAM5 During Similar Dynamics,” Journal of Geophysical Research Atmospheres 117, D15205. DOI: 10.1029/2012JD017589.