Long-term historic climate datasets are valuable tools to investigate climate variability, validate climate models and contextualize anticipated climate change. Surface solar radiation is one particularly relevant variable, with implications on policy decisions (e.g., performance of solar panels) and fundamental questions in climate science (e.g., regarding the energy budget). While all current twentieth century reanalyses provide surface solar radiation, we demonstrate that most of them fail to capture multidecadal surface radiation variability in Europe. To this end, we systematically compare the reanalyses 20CRv2c, 20CRv3, ERA20C and CERA20C and the free model run ERA20CM. We show that only CERA20C captures dimming (1949 - 1979) and brightening (1979 -2009) in line with station observations, satellite-era reanalyses and established theory. The lack of multidecadal surface radiation variability in 20CRv2c/v3 is plausible given the use of constant aerosols. In contrast, ERA20CM, ERA20C and CERA20C are forced with time-varying aerosols. Despite this common forcing, ERA20CM and ERA20C surprisingly show no trends in clear-sky fluxes over the dimming and brightening periods while CERA20C shows significant trends. We discuss different potential explanations for this discrepancy (model versions, ocean coupling and ensemble size) and conclude that none of them provides a convincing explanation. Our results therefore imply that only CERA20C is suitable for assessments of surface solar radiation variability on multi-decadal timescales. This particularly applies to impact studies, for example, on long-term potentials of solar power generation.

中文翻译：

---

在除 CERA20C 之外的所有百年再分析中都未能准确捕捉到欧洲的数十年太阳变化

长期历史气候数据集是研究气候变率、验证气候模型和将预期气候变化背景化的宝贵工具。地表太阳辐射是一个特别相关的变量，对政策决策（例如，太阳能电池板的性能）和气候科学的基本问题（例如，关于能源预算）具有影响。虽然当前所有 20 世纪的再分析都提供了地表太阳辐射，但我们证明其中大多数未能捕捉到欧洲数十年的地表辐射变化。为此，我们系统地比较了重新分析的 20CRv2c、20CRv3、ERA20C 和 CERA20C 以及免费模型运行的 ERA20CM。我们表明，只有 CERA20C 捕捉到与台站观测、卫星时代再分析和既定理论一致的变暗 (1949 - 1979) 和增亮 (1979 - 2009)。考虑到使用恒定气溶胶，在 20CRv2c/v3 中缺乏几十年的地表辐射变异是合理的。相比之下，ERA20CM、ERA20C 和 CERA20C 受时变气溶胶影响。尽管有这种共同的强迫，但 ERA20CM 和 ERA20C 在变暗和变亮期间出人意料地没有表现出晴天通量的趋势，而 CERA20C 则显示出显着的趋势。我们讨论了对这种差异的不同潜在解释（模型版本、海洋耦合和集合大小），并得出结论，它们都没有提供令人信服的解释。因此，我们的结果意味着只有 CERA20C 适合评估多年代际时间尺度上的地表太阳辐射变化。这尤其适用于影响研究，例如太阳能发电的长期潜力。