Abstract:

Based on climatic element data from the Hetao Plain collected between 1961 and 2017, a hybrid model was used to estimate the daily solar radiation in the Hetao Plain. Using a trend method, cumulative anomalies, an M-K test, wavelet analysis, cross wavelets, and other methods, the characteristics of solar radiation changes in the Hetao Plain were analyzed. Concurrently, the relationship with meteorological elements was also assessed. In the past 57 years, the annual average solar radiation received at the ground level in the Hetao Plain was 6030.83 MJ·m^-2, which represents slow decrease at a rate of 0.3 MJ·(10a)^-1. Seasonal characteristics were significant; the annual solar radiation was mainly concentrated in the summer (2138 MJ·m^-2) and was at its lowest levels in winter (793 MJ·m^-2). Furthermore, spring radiation showed a significant upward trend at a rate of 8.59 MJ·(10a)^-1, whereas summer and autumn radiation showed a slight downward trend, and winter radiation showed a significant downward trend at a rate of 7.06 MJ·(10a)^-1. The annual solar radiation mutation point in the Hetao Plain were in 1993; 1972 and 1993 were the spring mutation points; 1967 and 1997 were the summer mutation points; 2014 was the autumn mutation point; and 1984 was the winter mutation point. Wavelet analysis results show that 24 years was the main cycle of annual solar radiation in the Hetao Plain; the main periods of radiation were 27 years for spring and summer, 30 years for autumn, and 21 years for winter. Both the solar radiation and meteorological elements in the Hetao Plain had a 32-year resonance period. The number of hours of sunshine had the highest correlation with radiation followed by temperature and air pressure, whereas the correlation between relative humidity and radiation was relatively low. Temperature and solar radiation were mainly positively correlated on multiple time scales, e.g., 1986-1991 and 2001-2006. There was a positive correlation between air pressure and solar radiation from 1976 to 1981. Relative humidity and solar radiation were negatively correlated with two resonant periods of 8-16 and 16-32 years. There is a significant positive correlation between sunshine hours and solar radiation, and there were resonance high-value energy regions in the following periods: 1973-1981, 1986-1995, and 1997-2005.

Key words: solar radiation, variation characteristics, period, meteorological elements, Hetao Plain