In China, there is remarkable evidence that anthropogenic aerosol loading has dramatically and continuously increased over recent decades due to increased fossil fuel combustion [Ren et al., 1997; Qian et al., 2003]. Some studies show that the cooling trends over some areas of China are partly the result of increased man-made aerosol particles [Li et al., 1995; Qian et al., 1996, 2003; Qian and Giorgi, 2000; Xu, 2001]. On the other hand, it has been generally accepted that atmospheric aerosol particles not only affect climate directly by scattering and absorbing solar radiation, but also by modifying the microphysical and optical properties of clouds [Ramaswamy, 2001]. Rosenfeld et al. [2001] and Ackerman et al. [2003] found that increased aerosol can increase cloud droplet concentrations, thereby reducing cloud droplet size and precipitation efficiency. Therefore it is important to examine the nature of cloudiness changes over China over the past several decades. Has the marked increase of anthropogenic aerosols over China left a signature in the cloud observations?

Kaiser [1998, 2000] examined the variation of total cloud cover over China and found a general decreasing trend in annual mean cloud amount over much of the country from 1954–1994. In this paper we examined more meteorological variables and extended the time period of the analysis from 1954 to 2000, based on the newly available meteorological data from the China Meteorological Administration (CMA). Cloud fraction for total cloud and also low cloud, which is possibly more affected by aerosols, has been investigated for every month. Results show that the total cloud amount has a decreasing trend over northern China and an increasing trend in southern China during the dry season (September to April). The total cloud amount has a prevailing decreasing trend in both northern and southern China during the wet season (May to August). The variation of low cloud fraction shows a more inhomogeneous pattern and more stations with an increasing trend are found in northern China. We also analyzed the change in frequency of overcast sky and clear sky over the past 47 years in China. The relationship between total/low cloud fraction and Diurnal Temperature Range (DTR) is also discussed in this paper. Finally, a normalized cloud cover-surface air temperature relationship, NOCET, or dT/dCL, expressing temperature anomaly per unit deviation of total cloud cover or low cloud faction from its average [Sun et al., 2000], is used to further investigate the variations of the cloud properties and their effects on observed temperature change.

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