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) and evaluates its impact on simulated climate. The 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. This helps addressing the cold and excessive freezing biases in the CESM with respect to the actual observations. When spectral emissivities of sea ice and open ocean surfaces are considered, the broadband LW sea-ice emissivity feedback is indeed small, two orders of magnitude smaller than the surface albedo feedback. I will further describe ongoing effort to incorporate new ice-cloud optics and longwave scattering into the CESM and its impact on radiation budgets.
Prof. Xianglei Huang is currently a tenured associate professor and the Chair of graduate program at the Department of Climate and Space Sciences at the University of Michigan. He obtained his Ph.D. from Caltech and carried out his postdoctoral research at Princeton University. His research interest is atmospheric radiation, for applications in both satellite remote sensing and climate modeling. He has authored and co-authored 57 papers on premium journals including Science and PNAS. He is a recipient of 2015 NASA Langley's Henry J.E. Reid Award. He is a member of the Science Definition Team of NASA CLARREO mission, a co-Investigator for PREFIRE, a mission recently selected by NASA Earth Venture program, and a co-Investigator for FORUM, a European Space Agency mission under phase-A study for Earth Explorer 9. He also serves as an associate editor for Journal of Climate.