Most general circulation models compute radiation fluxes by assuming that water vapor is uniform within individual grid layers, which leads to an underestimation of satellite‐observed longwave (LW) cloud radiative forcing (LWCF). To fix this problem, we calculated water vapor content separately for clear and cloudy portions and used them to compute LW radiation. The impacts of this modification were examined by comparing two global simulations with and without the modification (NEW and OLD, respectively). Global‐annual mean LWCF from NEW was 1.8 W m⁻² higher than that of OLD, thus remedying a long‐standing negative bias of LWCF. This improvement is a combined result of more clear‐sky and less all‐sky upward LW flux at the top of the atmosphere than OLD. Large increases in LWCF and clear‐sky LW flux occurred in the tropical deep convection and midlatitude storm track regions where upper‐ and middle‐level clouds are abundant. Although only the LW radiation scheme was modified, global‐annual mean shortwave cloud radiative forcing also increased, particularly in the vicinity of the eastern subtropical marine stratocumulus decks through radiative feedback processes. With this improved treatment, it may be possible to tune general circulation models in a more flexible and physical way without introducing compensating errors.

中文翻译：

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一般循环模型中水汽亚网格变化对长波辐射的影响

大多数通用环流模型通过假设各个网格层中的水蒸气均匀来计算辐射通量，这会导致低估了卫星观测的长波（LW）云辐射强迫（LWCF）。为了解决这个问题，我们分别计算了晴和阴天部分的水蒸气含量，并用它们来计算LW辐射。通过比较带有和不带有修改的两个全局模拟（分别为NEW和OLD），检查了此修改的影响。来自NEW的全球年平均LWCF为1.8 W m ^-2高于OLD，从而纠正了LWCF长期存在的负偏差。这种改善是大气层顶部比旧大气层更高的晴空和更少的全天候上行LW通量的综合结果。在热带深对流和中纬度风暴路径区域，中高层云层丰富，LWCF和晴空LW通量大量增加。尽管仅修改了低辐射辐射方案，但全球年平均短波云辐射强迫也增加了，特别是在东部亚热带海洋平积层甲板附近，通过辐射反馈过程。通过这种改进的处理方法，可以在不引入补偿误差的情况下，以更灵活，更物理的方式调整常规循环模型。