RAPID: Evaluation of Multidecadal Variability in Surface Solar Radiation

这是由一封亲爱的同事来信(NSF 11-006)资助的16个快速反应(RAPID)项目之一，该信鼓励对为政府间气候变化专门委员会第五次评估报告(IPCC AR5)准备的气候模型模拟进行诊断分析。在这些项目中进行的研究有望导致更详细的模型相互比较，更好地理解稳健的模型行为，以及更好地理解和量化未来气候模拟中的不确定性。该项目旨在确定当前一代20世纪气候模拟是否能够重现观测到的地表日照记录，特别是太阳“变暗”和“变亮”的时期。虽然过去温室气体的辐射强迫是众所周知的，但气溶胶强迫--被认为是变暗和变亮的推定因素--的记录却并非如此。该项目的动机是，第四次评估报告(AR4)使用的前一代模型未能成功地再现欧洲和东亚地区观测到的变暗和变亮现象，这两个地区的早期研究表明，日晒趋势是由气溶胶而不是云层变化驱动的。鉴于观察到的趋势是由气溶胶驱动的，与模型的不一致表明，AR4模拟中使用的气溶胶历史并不准确，因此，在本项目试验中进行了研究，以改进AR4和AR5使用的模型之间的气溶胶驱动的日光可变性。这项工作依赖于一种在计算日照趋势时消除云层影响的新方法，这种方法很有用，因为模型没有与观测数据相同的云和天气历史。该项目的更广泛影响在于它支持政府间气候变化专门委员会第五次会议，该会议旨在向世界各地的决策者提供关于气候变化及其后果的信息。该项目特别寻求查明和减少气溶胶辐射强迫方面的不确定性，这将有助于减少有关地球气候对温室气体增加的敏感性的不确定性。

This is one of 16 Rapid Response (RAPID) projects funded as the result of a Dear Colleague Letter (NSF 11-006) encouraging diagnostic analyses of climate model simulations prepared for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Research conducted in these projects is expected to lead to more detailed model intercomparisons, better understanding of robust model behaviors, and better understanding and quantification of uncertainty in future climate simulations.This project seeks to determine whether the current generation of 20th century climate simulations can reproduce the observed record of surface insolation, particularly the periods of solar "dimming" and "brightening". While past radiative forcing by greenhouse gases is reasonably well known, the record of aerosol forcing - the presumed agent of dimming and brightening - is not. The project is motivated by the fact that the earlier generation of models used for the Fourth Assessment report (AR4) did not successfully reproduce the observed dimming and brightening over Europe and East Asia, two regions where earlier research shows that insolation trends were driven by aerosols rather than changes in clouds. Given that the observed trends were driven by aerosols, the lack of agreement with models suggests that the aerosol histories used in the AR4 simuations were not accurate, hence research in the present project tests for improvements in aerosol-driven insolation variability between models used for AR4 and AR5. The work relies on a novel method for the removal of cloud cover effects in the computation of insolation trends, which is useful since the models do not have the same cloud and weather history as the observations.The broader impact of the project lies in its support of the IPCC AR5, which is intended to provide information on climate change and its consequences to decision makers worldwide. This project seeks in particular to identify and reduce uncertainty in aerosol radiative forcing, which will contribute to reducing uncertainty regarding the sensitivity of earth's climate to greenhouse gas increases.