Climatic Characteristics of Gross Solar Radiation over Northwestern China
中国西北地区太阳总辐射的气候特征

With the trend analysis, Mann-Kendall and correlation analysis, the spatial and temporal distributions of gross solar radiation across Northwestern China were carefully examined using monthly mean data for the period 1961-2003 from 28 observational stations. It was shown that the gross solar radiation over the study region ranged roughly from 4300 to 7000 MJ/(m2·a). An increasing trend in the gross solar radiation from the southeast and the northwest to the middle regions was observed. Higher gross solar radiation values frequently occurred over the Qinghai plateau. As for the seasonality, the gross solar radiation in winter was the lowest, ranging from 185 to 400 MJ/m2. The gross solar radiation in summer was found highest, ranging from 540 to 750 MJ/m2. The gross solar radiation in spring falling between 400 and 685 MJ/m2 was greater than that in autumn, with a range from 290 to 530 MJ/m2. In addition, higher temporal stability in the gross solar radiation frequently took place over the regions with greater gross solar radiation. In general, the gross solar radiation across Northwestern China decreased at a rate of approximately 92.07 MJ/(m2·10a), with an abrupt change in the year 1973. The decreasing rate was largest over northern Xinjiang and the east of the area, showing two lowest decreasing rates around Turfan in Xinjiang and Xining City in Qinghai. Inter-annual gross solar radiation trends appeared to be similar with seasonal trends. The gross solar radiation was larger during the period from the 1960s to the 1970s; however, it achieved a minimum magnitude in the 1980s. In the 1990s, it increased to certain degree but basically lay in a small magnitude. This trend seems to be consistent with global trends. The Qinghai plateau displayed two-peak spatial distribution of gross solar radiation, showing a peak in May and the other in July, and a minimum value in January or February. It was indicated that cloud cover, relative humidity and precipitation can primarily affect the gross solar radiation over space but were not responsible for the observed decreasing trends in gross solar radiation. It was stated that the temperature and the gross solar radiation showed similar variation trends, which would likely result from increases in aerosol content in the atmosphere.