Assessing observed temperature and cloud amount trends for China over the last half of the Twentieth Century: What can the sunshine duration record tell us?

Analyses over recent years have shown that, like most nations with adequate observational data, temperatures over most of China have increased over the last half of the Twentieth Century. Most of this observed increase has been due to increases in daily minimum temperatures. Over this same period, cloud amount over China has been found to have decreased significantly. This is an interesting finding in that a trend towards less cloudiness over time would in itself be expected to cause minimum temperatures (usually occurring in the near dawn hours) to decrease over time due to enhanced radiational cooling near the surface. Obviously the causes of increasing temperature in general over China are not well understood at this time.

A study by Kaiser in the early 1990s, using data from 52 Chinese stations with monthly cloud amount and sunshine duration data, found evidence of decreasing cloudiness and decreasing sunshine duration. This seemingly curious result is still not understood completely; it perhaps can be partially explained by increasing air pollution causing the Campbell-Stokes Sunshine Recorder, which is sensitive to the intensity of direct solar radiation, to not record as much sunshine, especially early and late in the day when the atmospheric path length is greatest.

There is relatively high confidence in the findings from analysis of the cloud amount record, which most recently has been studied using 6-hourly observations from almost 200 station records provided by the China Meteorological Administration (CMA). The sunshine duration record has not received as much attention, so this study will examine daily sunshine duration data from these CMA stations, correlating the sunshine record with the cloud amount and temperature records on station by station, regional, and national levels, and also comparing decadal-scale variations and trends in sunshine duration with those of temperature and cloud amount.