Evaluation Of Clear-Sky Surface Downward Shortwave Fluxes Computed By Modtran6.0, Cccma, And Ceres Over Different Climatic Regimes
Presenter: Jordann Brendecke1
Co-Author(s): Xiquan Dong, Baike Xi, and Xiang Zhong
Advisor(s): Xiquan Dong
1Department of Hydrology and Atmospheric Sciences, University of Arizona
In this study, the clear-sky total, direct, and diffuse fluxes at the surface, are calculated from three radiation transfer models (RTMs) – MODTRAN6.0 (M6.0), Canadian Centre for Climate Modelling and Analysis (CCCma), and Fu-Liou (NASA CERES) – are evaluated against surface measurements collected from seven selected sites. These seven sites represent different climatological regimes and various surface scene types, including ocean, grassland/continental, desert, and snow/sea ice. Despite the exceptional decrease in computation time by CCCma, the statistical results from the two models show only small differences. While M6.0 shows closer means to observations, CCCma shows less standard deviation. Biases from CERES, M6.0, and CCCma are 0.9, 2.4, and 5.3 W m-2 in total flux across all samples. Even though CERES calculations outperform the M6.0 and CCCma in total flux, especially over desert scene types, this is offset by negative biases in direct (13.7 W m-2) and positive biases in diffuse (14.7 W m-2) across all scene types. Inputs such aerosol optical depth (AOD), aerosol optical properties, water vapor profile, and surface scene type are analyzed to explain some of the errors at certain sites. Future work will require more clear-sky days to compare against observations to build confidence for all-sky studies.