Abstract. Surface incident solar radiation (R_s) plays an essential role in climate change on Earth. R_s can be directly measured, and it shows substantial variability, i.e., global dimming and brightening, on decadal scales. R_s can also be derived from the observed sunshine duration (SunDu) with reliable accuracy. The SunDu-derived R_s was used as a reference to detect and adjust the inhomogeneity in the observed R_s. However, both the observed R_s and SunDu-derived R_s may have inhomogeneity. In Japan, SunDu has been measured since 1890, and Rs has been measured since 1961 at ~100 stations. In this study, the observed R_s and SunDu-derived R_s were first checked for inhomogeneity with a statistical software RHtest. If confirmed by the metadata of these observations, the detected inhomogeneity was adjusted based on the RHtest-quantile matching method. Second, the two homogenized time series were compared to detect further possible inhomogeneity. If confirmed by the independent ground-based observations of cloud cover fraction, the detected inhomogeneity was adjusted based on the reference dataset. As a result, a sharp decrease in the observed R_s from 1961 to 1975 caused by instrument displacement was detected and adjusted. Similarly, a gradual decline in SunDu-derived R_s due to steady instrument replacement from 1985 to 1990 was detected and adjusted. After homogenization, the two estimates agree well. R_s was found to have increased at a rate of 0.9 W m⁻² per decade (p < 0.01) from 1961 to 2015 based on the homogenized SunDu-derived R_s, which was enhanced by a positive aerosol-related radiative effect (2.2 W m⁻² per decade) and diminished by a negative cloud cover radiative effect (−1.4 W m⁻² per decade). The brightening over Japan was the strongest in spring, likely due to a significant decline in aerosol transported from Asian dust storms. The observed raw R_s data and their homogenized time series used in this study are available at https://doi.org/10.11888/Meteoro.tpdc.271524 (Ma et al., 2021).

中文翻译：

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日本上空均匀的百年地表入射太阳辐射

摘要。地表入射太阳辐射 ( R _s ) 在地球气候变化中起着至关重要的作用。R _s可以直接测量，并且它在年代际尺度上显示出显着的可变性，即全局变暗和变亮。R _s也可以从观测到的日照时数 (SunDu) 中以可靠的精度推导出来。SunDu 衍生的R _s用作检测和调整观察到的R _{s 中}的不均匀性的参考。然而，观察到的R _s和 SunDu 派生的R _s可能有不均匀性。在日本，自 1890 年以来一直在测量 SunDu，自 1961 年以来一直在大约 100 个站点测量 Rs。在这项研究中，首先使用统计软件 RHtest 检查观察到的R _s和 SunDu 衍生的R _s的不均匀性。如果通过这些观察的元数据确认，则根据 RHtest-quantile 匹配方法调整检测到的不均匀性。其次，比较两个同质化的时间序列以检测进一步可能的不均匀性。如果云覆盖率的独立地面观测证实，检测到的不均匀性将根据参考数据集进行调整。结果，观察到的R _s急剧下降1961年至1975年对仪器位移引起的进行检测和调整。同样，由于从 1985 年到 1990 年稳定的仪器更换，SunDu 衍生的R _s逐渐下降被检测到并进行了调整。均质化后，两个估计值吻合得很好。ř_小号被发现的为0.9W米的速率增加^-2基于从1961年每十（P <0.01），以2015匀浆SunDu衍生ř_小号（，将其通过正的气溶胶有关的辐射效应提高2.2 W m ^-2每十年）并因负云覆盖辐射效应而减少（-1.4 W m ^-2每十年）。日本上空的增亮在春季最为强烈，可能是由于亚洲沙尘暴传播的气溶胶显着减少。观察到的原始R _s数据及其在本研究中使用的均质化时间序列可在 https://doi.org/10.11888/Meteoro.tpdc.271524（Ma 等人，2021 年）获得。