中文摘要：

利用1961-2008年北京城区和郊区12个台站的气候观测资料，采用趋势分析和累积距平的方法，研究了北京城区和郊区近48年的日照时数、总云量及低云量的年际和四季变化趋势，并探讨了城市化进程对日照和云量变化的影响。结果表明：近48年来，城区的总云量和日照时数呈减少趋势，但低云量呈增加趋势；郊区的总云量和低云量呈增加趋势，而日照时数呈减少趋势；具体到年代变化，1980年代初以后，城区总云量呈减少趋势，且1990年代减少的趋势最为明显，2000年后，城区总云量变化发生逆转，呈显著增加趋势。对于低云量，1960年代到1980年代，城区郊区低云量呈波动减少趋势，而1990年代到2000年代后呈波动增加趋势。对于日照时数，1960年代到1980年代城区郊区日照时数均呈增加趋势，1990年代至2000年代则呈明显减少的趋势。低云量与日照时数表现出明显负相关特征，这与北京城市化发展对区域气候的影响有密切的关系。

英文摘要：

The authors study the seasonal and interannual variations of sunshine duration, total cloud cover amount, and low cloud cover amount in the past 48 years for both the urban and suburban areas in Beijing by utili zing the observational data from 1961 to 2008 at 12 stations in the urban and suburban areas and by employing the methods of trend analysis and accumulation bias, and also discuss the effects of urbanization on the variations of sun- shine duration and cloud cover amount. For the urban area, the results have shown a decreasing trend for the total cloud cover amount, but an increasing trend for the sunshine duration. For the suburban area, the results have shown an increasing trend for the total and low cloud cover amount, but a decreasing trend for the sunshine duration. In decadal scale for these variations, the total cloud cover amount for the urban area has decreased since the beginning of the 1980s, especially in the 1990s. After 2000, the total cloud cover amount for the urban area has reversed and increased significantly, however, the low cloud cover amount for both urban and suburban areas has shown a decrea- sing trend with fluctuation from the 1960s to the 1980s, but an increasing trend with fluctuation from the 1990s to the 2000s. The sunshine duration for both urban and suburban areas has shown an increasing trend from the 1960s to the 1980s, but a decreasing trend from the 1990s to the 2000s. The low cloud cover amount and the sunshine duration show a negative relationship. This is closely related to the effects of urbanization on regional climate.