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  • Gorodetskaya, I. V., B.-L. Tremblay, B. Liepert, M. A. Cane, and R. I. Cullather, 2008: The Influence of Cloud and Surface Properties on the Arctic Ocean Shortwave Radiation Budget in Coupled Models. J. Climate. In press.

We analyze the impact of Arctic sea ice concentrations, surface albedo, cloud fraction, and cloud ice and liquid water paths on the surface and top-of-atmosphere short-wave radiation budget in the 20th century simulations of three coupled models participating in the IPCC 4th Assessment Report. The models are: Goddard Institute for Space Studies ModelE Version R (GISS-ER), the UK Met Office Hadley Centre Model (UKMO HadCM3), and the National Center for Atmosphere Research Climate Community System Model (NCAR CCSM3). The models agree with each other and with observations of high Arctic mean cloud fraction in summer, however, large differences are found in the cloud ice and liquid water contents. Of the three models analyzed, the simulated Arctic clouds of the CCSM3 model have the highest liquid water content, exceeding the observed values. The clouds in the GISS-ER model are characterized by extremely high ice content and little liquid water content, and the HadCM3 model clouds hold moderate amounts of ice and relatively small amounts of liquid water. In the CCSM3 model, the high surface albedo and strong cloud short-wave radiative forcing both significantly decrease the amount of short-wave radiation absorbed by the Arctic Ocean surface during the summer. In the GISS-ER and HadCM3 models, the surface and cloud effects compensate: the first model with higher summer surface albedo has a larger downwelling short-wave flux, compared to the latter model with the lower surface albedo. Due to the differences in the models' cloud and surface properties, the Arctic Ocean surface gains about 20\% and 40\% more energy during the melt period in the GISS-ER and HadCM3 models, respectively, compared to the CCSM3 model. The HadCM3 model shows the largest reduction in both the sea ice area and volume during the summer consistent with the largest surface net short-wave radiation. In GISS-ER large winter sea ice thickness impairs the sea ice area reduction during the melt period counteracting the excessive net short-wave flux, while CCSM3 shows a significant decrease in both the sea ice area and volume during the summer despite the net short-wave flux deficiency. Substantial decrease in the sea ice area predicted by the end of the 21st Century in the CCSM3 model is associated with the large drop in the surface albedo, which is only partly compensated by the increased cloud short-wave forcing. In the HadCM3 and GISS-ER models, however, the compensation of the surface albedo and cloud short-wave forcing effects is one of the factors explaining moderate future sea ice volume trends.


Full Article: http://www.ldeo.columbia.edu/res/div/ocp/pub/gorodetskaya/irina_ipccpaper.pdf

Last Updated: 2008-02-06

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