Cloud scattering impact on thermal radiative transfer and global longwave radiation

• Published in: Journal of quantitative spectroscopy & radiative transfer 2019-12, Vol.239, p.106669, Article 106669
• Main Authors: Jin, Zhonghai, Zhang, Yuanchong, Del Genio, Anthony, Schmidt, Gavin, Kelley, Maxwell
• Format: Article
• Language: English
• Subjects: Longwave cloud scattering; Longwave radiation; Meteorology And Climatology; Radiative transfer
• ISSN: 0022-4073; 1879-1352
• DOI: 10.1016/j.jqsrt.2019.106669

•LW cloud scattering effect on radiation fluxes and its spectral variation and dependence on cloud properties are investigated.•An efficient radiative transfer scheme to explicitly consider the LW scattering is implemented to the GISS GCM for accurate calculation of radiation.•LW cloud scattering effect is nonnegligible in climate modeling. The potential importance of longwave (LW) cloud scattering has been recognized but the actual estimate of this effect on thermal radiation varies greatly among different studies. General circulation models (GCMs) generally neglect or simplify the multiple scattering in the LW. In this study, we use a rigorous radiative transfer algorithm to explicitly consider LW multiple-scattering and apply the GCM to quantify the impact of cloud LW scattering on thermal radiation fluxes. Our study shows that the cloud scattering effect on downward thermal radiation at the surface is concentrated in the infrared atmospheric window spectrum (800–1250 cm−1). The scattering effect on the outgoing longwave radiation (OLR) is also present in the window region over low clouds but it is mainly in the far-infrared spectrum (300–600 cm−1) over high clouds. For clouds with small to moderate optical depth (τ