Continued research on observed changes in cloudiness and air pollution over China and their relationships with other meteorological variables

Climate research conducted in recent years has shown China to be quite a unique region of the globe in terms of observed variability and trends in many primary meteorological variables. Indeed, in several ways, eastern China, especially, seems to demonstrate changes that are opposite in sign of those observed over other mid-latitude land regions of the northern hemisphere. The main variable that may be characterized as such is total cloud cover (TCC). Several studies [e.g., Kaiser (1998; 2000); Kaiser and Qian (2002)] have shown that most of China has experienced a decrease in TCC over the last half of the twentieth century, whereas most other land areas of the globe with surface-observed cloud data that show any significant change have shown increases [e.g., Angel (1990) for the United States; Jones and Henderson-Sellers (1992) for Australia]. The decrease in cloudiness over China is made even more interesting (indeed, perplexing) by the concomitant decrease in sunshine duration that is also found [Kaiser and Qian (2002)]. Normally one would of course expect that a long-term decrease in cloud amount would result in an increase in sunshine duration, but this has not been observed for China. The marked decrease in sunshine duration described in Kaiser and Qian (2002) has been attributed to well-documented increases in atmospheric anthropogenic aerosol loading (mainly sulfate) over China during recent decades due to increased fossil fuel combustion. These aerosols produce haze that is thought to enhance the backscatter and absorption of incoming solar radiation and thus weaken the direct solar radiation needed to activate the sunshine recorder, especially early and late in the day when the atmospheric path length is greater. A related question still to be resolved is: How might this increased atmospheric haze affect the ability of surface observers to estimate the fraction of the celestial dome covered by clouds? Could the increased haze at least in part be responsible for the decreasing trend in TCC? In this presentation we will attempt to answer this question by comparing the surface-observed TCC record over China with ISCCP satellite observations available for the common data period of 1984-2002. While it is known that satellite estimates of TCC are typically greater than concurrent surface-observed TCC, we will be comparing the correlation and trends from the two records in order to see if they differ in such a way as to explain any effect the aerosol haze might have on the surface-based observations. We will also present updates of and examine relationships between several other primary meteorological variables for China, such as near-surface air temperature, precipitation, evaporation, relative humidity, soil moisture, and solar irradiance. Along with looking at things at the individual station level and at the country level, as in our past analyses of Chinese climate, we will also use a gridded analysis to depict trends, correlations, and their statistical significance.

REFERENCES Angel, J. K., Variations in United States cloudiness and sunshine duration between 1950 and the drought year of 1988, J. Climate, 3, 296-308, 1990.

Jones, P. A., and A. Henderson-Sellers, Historical records of cloudiness and sunshine in Australia, J. Climate, 5, 260-267, 1992.

Kaiser, D. P., Analysis of total cloud amount over China, 1951–1994. Geophys. Res. Lett. 25, 3599–3602, 1998.

Kaiser, D. P., Decreasing cloudiness over China: An updated analysis examining additional variables. Geophys. Res. Lett. 27, 2193–2196, 2000.

Kaiser, D. P. and Qian, Y. Decreasing trends in sunshine duration over China for 1954–1998: Indication of increased haze pollution? Geophys. Res. Lett. 29, 2042, doi:10.1029/2002GL016057, 2002.