Decreasing Cloudiness Over China: An Updated Analysis Examining Additional Variables

The compilation of a 6-hourly database of meteorological observations (196 stations) by the China Meteorological Administration (CMA) has made possible many studies in recent years examining climatic change over China since the early 1950s. One recent study examined the total cloud amount record over China from 1951-1994 and found evidence for significant decreases in total cloud amount over much of the country. In the current analysis, additional cloud amount data from 191 of the CMA stations have been obtained through synoptic reports collected for a soon to be released global cloudiness database (U. Arizona/U. Washington/U.S. Dept. of Energy), extending the analysis through 1996. To better characterize the nature of the observed cloud decreases over China, other variables such as water vapor pressure, relative humidity, and station air pressure have also been examined. Station air pressure has increased significantly over most of China, and in the areas showing the strongest cloud amount decreases, relative humidity has also decreased. A 1954-1996 time series of midday total cloud amount for China as a whole has been constructed and its linear trend is -0.8% sky cover per decade (see figure).

It is interesting to note that the significant decreases in total cloud amount over China since the early 1950s are unique amongst the trends analyzed from the various national cloud data sets made available in recent years (e.g., for the former USSR, United States, and Australia). An intriguing aspect of the all-China cloud amount time series (station air pressure time series) is a rather abrupt decrease (increase) in annual mean values around 1977/1978. This change coincides closely with the large increase in global mean temperatures identified in the literature in recent years (mainly driven by increases in minimum temperature), which in turn coincides with what has been described by the IPCC as a fundamental shift in the ENSO phenomenon at about this same time.