Determining Factors of Monthly to Decadal Variability in Surface Solar Radiation in China: Evidences From Current Reanalyses

Clouds and aerosols play essential roles in regulating surface incident solar radiation (R-s). It has been suggested that the increased aerosol loading over China is a key factor for the decadal variability in R-s and can explain the bias in its trend from reanalyses because the reanalyses do not include the interannual variability of aerosols. In this study, we compare the R-s derived from sunshine duration at 2,400 weather stations in China and that from five reanalyses from 1980 to 2014. The determining factors for the biases in the mean values and trends of R-s from the reanalyses are examined, with the help of R-s and the cloud fraction (CF), from satellite and 2,400 weather stations. Our results show that all reanalyses overestimate the multiyear R-s by 24.10-40.00 W/m(2) due to their underestimations of CF, which is more obvious in southern China. The biases in the simulated CF in the reanalyses can explain the biases in R-s by 55-41%, and the bias in clear-sky surface solar radiation (R-c), which is primarily due to biases in aerosol loading, can explain 32-9% of the bias in R-s. The errors in the trend of the simulated CF can explain the errors in the R-s trends in the reanalyses by 73-12%, and the trend errors in the R-c can explain 43-30% of the trend error in R-s. Our study suggests that more work is needed to improve the simulation of aerosols, clouds, and aerosol-cloud-radiation interactions in the reanalyses.