Simulation of Arctic Climate with the Regional Arctic System Model (RASM): Sensitivity to Atmospheric Processes

John J Cassano1, Alice K DuVivier2, Mimi Abel3, Andrew Roberts4, Michael Brunke5, Anthony Craig6, Brandon J Fisel7, William J Gutowski Jr8, Wieslaw Maslowski9, Bart Nijssen10, Robert Osinski9 and Xubin Zeng5, (1)Univ Colorado, Boulder, United States, (2)NCAR, Boulder, United States, (3)University of Colorado at Boulder, Boulder, CO, United States, (4)Lost Alamos National Laboratory, Los Alamos, United States, (5)University of Arizona, Department of Hydrology and Atmospheric Sciences, Tucson, AZ, United States, (6)Naval Postgraduate School, Monterey, United States, (7)Iowa State University, Ames, IA, United States, (8)Iowa State Univ, Department of the Earth, Atmosphere, and Climate, Ames, United States, (9)Naval Postgraduate School, Monterey, CA, United States, (10)University of Washington Seattle Campus, Seattle, WA, United States
Abstract:
A new regional Earth system model of the Arctic, the Regional Arctic System Model (RASM), has recently been developed. The initial version of this model includes atmosphere (WRF), ocean (POP), sea ice (CICE), and land (VIC) component models coupled with the NCAR CESM CPL7 coupler. The model is configured to run on a large pan-Arctic domain that includes all sea ice covered waters in the Northern Hemisphere and all Arctic Ocean draining land areas.

Results from multi-decadal (1979 to present) simulations with RASM will be presented and will focus on the model climate's sensitivity to atmospheric processes and a comparison of the fully coupled model and atmosphere-only simulations. The modeled radiation budget, and sea ice cover, was found to be sensitive to the details of the cloud and radiation parameterizations in the atmospheric component (WRF) of RASM, including details of cloud droplet size. Another model sensitivity was found in relation to atmosphere-land processes. Care is needed to ensure that decoupling between the atmosphere and land do not occur under strongly stable conditions over land areas in winter.

Comparison of RASM near surface climate with that simulated with stand-alone WRF show areas of both improved and degraded results. Improvement in the coupled model climate are related to more physically realistic representation of coupled processes such as energy transfer from the ocean to the atmosphere through leads in the sea ice during winter. Degraded results come from feedbacks in model component biases, such as atmospheric circulation biases resulting in incorrect local sea ice cover that then result in large local atmospheric temperature biases.

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