Comparison of Ice Cloud Radiative Effects Simulated By RRTMG, Fu-Liou RTM, and LBLRTM-DISORT

Comparison of ice cloud radiative effects simulated by RRTMG, Fu-Liou RTM, and LBLRTM-DISORT

Boyan Gu, ¹ Ping Yang, ¹ Kenneth Bowman, ¹ Eli Mlawer²

 

1. Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843, USA
2. Atmospheric and Environmental Research (AER), Lexington, MA 02421, USA

Ice clouds play an important role in climate system, especially in the Earth's radiation balance and hydrological cycle. Although there are a number of theoretical and experimental studies about the radiative effects of ice clouds, the representation of ice clouds in numerical models is still subject to significant uncertainties. We use a combination of line-by-line radiative transfer model (LBLRTM) and discrete ordinate radiative transfer model (DISORT) as the benchmark model (accurate but computationally intensive) to calculate radiative fluxes under clear and cloudy skies in the spectral region of 0.2-1000μm, and compare the results with the counterparts based on the rapid radiative transfer model for GCM applications (RRTMG) and Fu-Liou radiative transfer model. Ice cloud radiative effects (considering both absorption and scattering) in both single column and global simulations for RRTMG and Fu-Liou RTM are quantified using the MODIS collection 6 ice cloud retrieval products. Sensitivity tests are also carried out to determine the spectral resolution that achieves the optimal balance between computational efficiencies and accuracies for the purposes of ice cloud radiative effect simulations with the rigorous method.