Analysis of total cloud amount over China, 1951-1994

Trends in Chinese total cloud amount were analyzed for the period 1951-1994. Cloud data were obtained from a database of 6-hourly weather observations provided by the China Meteorological Administration (CMA) to the U.S. Department of Energy's Carbon Dioxide Information Analysis Center (CDIAC) through a bilateral research agreement. Seasonal and annual means of midday (1400 Beijing Time (BT)) and midnight (0200 BT) observations were computed for each of 196 stations and over 8 specific regions of China. Linear regression analysis was used to characterize seasonal and annual trends in total cloud amount from 1951-1994. Decreasing trends in both midday and midnight cloud amount are observed over much of China; most stations in central, eastern, and northeastern China show statistically significant decreases of 1-3% sky cover per decade. These decreases in cloud amount are especially interesting in light of recent temperature trends observed over China. Several studies have shown significant increasing trends in daily minimum temperatures over China since 1951, especially in the northeastern part of the country, precisely where the strongest decreasing trends in total cloud amount are observed. Increases in cloud amount have been offered as a possible explanation for increasing minimum temperatures in other parts of the world; however, in China it seems that some mechanism(s) other than increasing cloud amount must be considered for understanding the observed increase in minimum temperatures.