Decreasing trend of sunshine hours and related driving forces in North China

Global dimming is currently an active area of research in climate change. Trends of temporal (on the order of decades, years, seasons or even months) and spatial patterns in sunshine hours and associated climatic factors (average air temperature, relative humidity, precipitation and wind speed) over North China are evaluated for the period 1965 similar to 1999 based on data from 81 standard meteorological stations. The results show that: (1) North China is experiencing decreasing sunshine hours (-82.855 h/decade); (2) seasonally, decline in sunshine hours is highest in summer and lowest in winter; (3) spatially, decrease in sunshine hours is highest in inland and plain regions and lowest in the northwest mountain and coastland regions; (4) sunshine hours have a high correlation with precipitation, relative humidity and wind speed, with wind speed having the strongest influence on sunshine hours implicit in the close correlation (temporally and spatially) between the two variables; (5) cloud cover could not be any significant driver of sunshine-hour decline because it is more or less stable; (6) spatially and seasonally, wind speed is an important driving factor of decreasing sunshine hours in North China. Furthermore, the interactions between wind speed and aerosol loading may be an enabling factor of wind speed in driving (strongly) the changes in sunshine hours.