Improved Representation of Surface Spectral Emissivity in a Global Climate Model and Its Impact on Simulated Climate

Journal Article · 01 May 2018 · Journal of Climate

DOI: https://doi.org/10.1175/JCLI-D-17-0125.1 · OSTI ID:1432584

Huang, Xianglei ^[1]; Chen, Xiuhong ^[1]; Flanner, Mark ^[1]; Yang, Ping ^[2]; Feldman, Daniel ^[3]; Kuo, Chaincy ^[3]

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1. Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, Michigan
2. Department of Atmospheric Sciences, Texas A&M University, College Station, Texas
3. Division of Climate and Ecosystem Sciences, Lawrence Berkeley Laboratory, Berkeley, California

Surface longwave emissivity can be less than unity and vary significantly with frequency. However, most climate models still assume a blackbody surface in the longwave (LW) radiation scheme of their atmosphere models. This study incorporates realistic surface spectral emissivity into the atmospheric component of the Community Earth System Model (CESM), version 1.1.1, and evaluates its impact on simulated climate. By ensuring consistency of the broadband surface longwave flux across different components of the CESM, the top-of-the-atmosphere (TOA) energy balance in the modified model can be attained without retuning the model. Inclusion of surface spectral emissivity, however, leads to a decrease of net upward longwave flux at the surface and a comparable increase of latent heat flux. Global-mean surface temperature difference between the modified and standard CESM simulation is 0.20 K for the fully coupled run and 0.45 K for the slab-ocean run. Noticeable surface temperature differences between the modified and standard CESM simulations are seen over the Sahara Desert and polar regions. Accordingly, the climatological mean sea ice fraction in the modified CESM simulation can be less than that in the standard CESM simulation by as much as 0.1 in some regions. When spectral emissivities of sea ice and open ocean surfaces are considered, the broadband LW sea ice emissivity feedback is estimated to be −0.003 W m ⁻² K ⁻¹ , assuming flat ice emissivity as sea ice emissivity, and 0.002 W m ⁻² K ⁻¹ , assuming coarse snow emissivity as sea ice emissivity, which are two orders of magnitude smaller than the surface albedo feedback.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
• Grant/Contract Number: AC02-05CH11231; SC0012969; SC0013080
• OSTI ID: 1432584
• Journal Information: Journal of Climate, Journal Name: Journal of Climate Journal Issue: 9 Vol. 31; ISSN 0894-8755
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English