Because the forcings to which Coupled Model Intercomparison Project - Phase 5 (CMIP5) models were subjected were poorly quantified, recent efforts from the Radiative Forcing Model Intercomparison Project (RFMIP) have focused on developing and testing models with exacting benchmarks. Here, we focus on aerosol forcing to understand if for a given distribution of aerosols, participating models are producing a radiometrically-accurate forcing. We apply the RFMIP experimental protocol for assessing flux biases in aerosol instantaneous radiative effect (IRE) on two participating models, GFDL AM4 and CESM 1.2.2. The latter model contains the RRTMG radiation code which is widely used among CMIP6 GCM's. We conduct a series of calculations that test different potential sources of error in these models relative to line-by-line benchmarks. We find two primary sources of error: two-stream solution methods and the techniques to resolve spectral dependencies of absorption and scattering across the solar spectrum. The former is the dominant source of error for both models but the latter is more significant as a contributing factor for CESM 1.2.2. Either source of error can be addressed in future model development, and these results both demonstrate how the RFMIP protocol can help determine the origins of parameterized errors relative to their equivalent benchmark calculations for participating models, as well as highlight a viable path towards a more rigorous quantification and control of forcings for future CMIP exercises.

中文翻译：

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对两种地球系统模型中短波参数化计算的瞬时气溶胶辐射效应偏差的研究

由于耦合模型比对项目 - 第 5 阶段 (CMIP5) 模型所承受的强迫没有得到很好的量化，因此辐射强迫模型比对项目 (RFMIP) 最近的工作重点是开发和测试具有严格基准的模型。在这里，我们专注于气溶胶强迫，以了解对于给定的气溶胶分布，参与模型是否正在产生辐射测量准确的强迫。我们应用 RFMIP 实验协议来评估气溶胶瞬时辐射效应 (IRE) 中两个参与模型的通量偏差，GFDL AM4 和 CESM 1.2.2。后一个模型包含在 CMIP6 GCM 中广泛使用的 RRTMG 辐射代码。我们进行了一系列计算，以测试这些模型中相对于逐行基准的不同潜在误差源。我们发现了两个主要的误差来源：双流解法和解决整个太阳光谱吸收和散射的光谱依赖性的技术。前者是两种模型的主要误差来源，但后者作为 CESM 1.2.2 的影响因素更为重要。在未来的模型开发中可以解决任何一种错误来源，这些结果都证明了 RFMIP 协议如何帮助确定与参与模型的等效基准计算相关的参数化错误的来源，并突出了通往更严格的可行路径量化和控制未来 CMIP 练习的强迫。前者是两种模型的主要误差来源，但后者作为 CESM 1.2.2 的影响因素更为重要。在未来的模型开发中可以解决任何一种错误来源，这些结果都证明了 RFMIP 协议如何帮助确定与参与模型的等效基准计算相关的参数化错误的来源，并突出了通往更严格的可行路径量化和控制未来 CMIP 练习的强迫。前者是两种模型的主要误差来源，但后者作为 CESM 1.2.2 的影响因素更为重要。在未来的模型开发中可以解决任何一种错误来源，这些结果都证明了 RFMIP 协议如何帮助确定与参与模型的等效基准计算相关的参数化错误的来源，并突出了通往更严格的可行路径量化和控制未来 CMIP 练习的强迫。