Climatic Trend of Cloud Amount Related to the Aerosol Characteristics in Beijing During 1950-2005

This paper analyzes the correlation between variations of total and low cloud amounts and the varying features of aerosols related to urban development of Beijing by using the cubic spline fitting method based on the monthly meteorological data of temperature, humidity, precipitation, clouds, and aerosol optical depth (AOD) during 1950-2005. The statistics on the development of the city of Beijing in this period, including the total industrial output, population, residential housing development, highway construction, charcoal production, etc., is revealed. Accompanying the rapid urban development of Beijing over the past 55 years or so, the urban aerosol concentration and composition have changed. The results indicate that: 1) there is a general trend of climate warming and drying in Beijing; 2) the total cloud amount in all seasons declines drastically, but lower cloud amount climbs up slightly; 3) the high correlations between cloud amount and the indices of Beijing urban development such as the housing area, charcoal production, and road construction show that the variation of cloud amount is closely related to the urban development; 4) the changing trend of AOD coincides more closely with the variation of low cloud amount. The evident drop of total cloud amount is in agreement with the trend of climate warming and drying, while the slight growth of low cloud amount is likely caused by more haze and fog occurrences in the lower troposphere in association with the pollution responsible for the "darkening" of Beijing and the surrounding areas.