In this study the clear-sky total, direct, and diffuse shortwave (SW) fluxes at the surface, have been calculated by three radiation transfer models (RTMs) – MODTRAN6.0 (M6.0), Canadian Centre for Climate Modelling and Analysis (CCCma), and Langley-modified Fu-Liou (NASA CERES). These calculations have been evaluated by surface measurements collected from seven sites that represent different climatological regimes with various surface scene types including ocean, grassland/continental, desert, and snow/sea ice. For pristine atmospheric conditions, SW fluxes predicted by CCCma and M6.0 shows little variation, which lays a baseline for further analysis. Note that computing time required by CCCma is ∼1000 times smaller than M6.0. Based on all samples collected from seven sites, mean differences of total, direct, and diffuse fluxes between surface measurements and CCCma / M6.0 / Fu-Liou are [5.3 / 2.4 / 0.9], [-2.2 / -5.1 / -13.7], and [7.5 / 7.5 / 14.6] W m, respectively. Histograms of differences between the three RTM calculations and surface measurements show that CCCma computed direct and diffuse fluxes have the smallest biases with standard deviations similar to those for M6.0, while Fu-Liou values have the largest biases and standard deviations. While Fu-Liou outperforms for total flux, especially for desert conditions, it is hampered by large biases for direct and diffuse across all scene types. The three RTMs are consistent with showing the least error for total flux and the largest in diffuse based on bias, correlation, and root mean square error.

中文翻译：

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三种大气辐射传输模型计算的晴空表面下降短波通量的评估


在这项研究中，晴空表面的总通量、直射通量和漫射短波 (SW) 通量已通过三个辐射传输模型 (RTM) 进行了计算 - MODTRAN6.0 (M6.0)、加拿大气候建模与分析中心（CCCma）和兰利修改的 Fu-Liou（NASA CERES）。这些计算已通过从七个地点收集的表面测量进行了评估，这些地点代表了具有各种表面场景类型的不同气候状况，包括海洋、草原/大陆、沙漠和雪/海冰。对于原始大气条件，CCCma和M6.0预测的SW通量变化不大，这为进一步分析奠定了基线。请注意，CCCma 所需的计算时间比 M6.0 小约 1000 倍。根据从七个地点收集的所有样本，表面测量与 CCCma / M6.0 / Fu-Liou 之间的总通量、直接通量和漫射通量的平均差异为 [5.3 / 2.4 / 0.9]、[-2.2 / -5.1 / -13.7 ] 和 [7.5 / 7.5 / 14.6] W·m 分别。三种 RTM 计算和表面测量之间的差异直方图表明，CCCma 计算的直接通量和漫射通量具有最小的偏差，标准偏差与 M6.0 相似，而 Fu-Liou 值具有最大的偏差和标准偏差。虽然 Fu-Liou 在总通量方面表现出色，尤其是在沙漠条件下，但它受到所有场景类型中直接和漫射的大偏差的阻碍。基于偏差、相关性和均方根误差，这三个 RTM 与显示总通量的最小误差和漫反射的最大误差一致。