Using the CAM5 Physics in WRF to Better Understand Physics Behavior Across Scales

Wednesday, May 14, 2014 - 07:00
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The atmospheric physics from the Community Atmosphere Model v5.1 (CAM5) have been ported into the Weather Research and Forecasting (WRF) model to enable evaluation of the parameterization suite across resolutions and contrast those parameterizations with those used routinely in high resolution models. The CAM5 components available in WRF now include clouds, turbulence, radiation, and aerosols, which enable one to run WRF with atmospheric physics almost identical to those used in the global CAM5. WRF's ability to easily change resolution has permitted efficient analysis of resolution dependence. The limited area nature of the WRF model grids also allows one to constrain the large-scale meteorological conditions through prescribed boundary conditions while permitting the physics to freely operate in the domain interior. This compliments the nudging technique occasionally employed with the global CAM5, which constrains meteorological fields through nudging and therefore only allows some of the physics to freely operate. There are many opportunities provided by this new capability including quickening parameterization development and providing a way to efficiently analyze resolution dependence, and we highlight three examples of projects that have taken advantage of this capability. First, an investigation of black carbon transport into the Arctic showed that increasing resolution also increases transport of black carbon from East Asia to the North American Arctic. Second, a comparison of the resolution dependence of the Morrison-Gettelman and Morrison microphysics parameterizations showed noticeably different resolution sensitivity. And third, a study of the precipitation characteristics generated by the CAM5 physics at mesoscale resolution documented the trade-off between having an accurate precipitation mean versus an accurate precipitation diurnal cycle over the central United States with the Zhang McFarlane deep convective parameterization. The adaptability of the WRF environment and ability to easily compare WRF results with observations, using tools such as the Aerosol Modeling Testbed, will ultimately result in quicker parameterization development for CAM5 and its predecessors as the physics improvements are first examined regionally in WRF and then applied globally in the global model.