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.
基于10个地面气象站资料，本文对中国东部地区20世纪上半叶日照时数及总云量的短期变率及长期趋势进行了研究。同时也分析了日照时数分别与温度日较差、总云量的相关性。结果表明中国东部也存在着早期变亮现象，日照时数在1908至1936年间呈上升趋势（0.16小时/日/十年），其中秋季的上升幅度最大（0.33小时/日/十年）。日照时数与温度日较差较好的正相关关系（相关系数达0.72）表明了日照时数的观测是可信的。总云量呈现下降趋势（-0.93%/十年）且与日照时数呈现明显负相关（-0.74），表明日照时数的变化贡献来自于云量的变化。该研究结果明显不同于1960年代以来云量不能解释中国地区地表太阳辐射变化。