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Interannual and Decadal Variations of Surface Solar Radiation over East China in the First Half of the 20th Century

Abstract Variability and long-term trends of sunshine duration (SSD) and total cloud cover (TCC) were studied based on surface observations from 10 meteorological stations over East China in the first half of the 20th century. The correlation coefficients between SSD and diurnal temperature range (DTR), as well as TCC, were analyzed. SSD experienced a significant increasing trend (0.16 h d−1 per decade) from 1908 to 1936, and the maximum brightening was in autumn (0.33 h d−1 per decade). The good agreement between the variability of SSD and DTR, supported by the correlation coefficient between them of 0.72, implies that the SSD measurements were reliable. TCC showed a decreasing trend (-0.93% per decade) and was significantly inversely related to SSD (-0.74), indicating the variation of SSD was attributable to changes in cloud cover. The result was obviously different to that since the 1960s, when clouds could not account for the decadal trend of surface solar radiation in China.