Evaluation of the Total, Direct, and Diffuse Solar Radiations From the ERA5 Reanalysis Data in China

Surface solar radiation is essential for regional climate and environmental research. The widely used European Centre for Medium-Range Weather Forecasts ERA5 reanalysis products provide long-term spatial estimates of the total and direct solar radiation on an hourly scale; however, its accuracy has not been systematically evaluated for China. In this letter, in situ measurements from 98 sites are used to analyze the deviations in the hourly radiation from ERA5 and to compare the daily variations. The results reveal that estimates from the reanalysis correlate well with ground observations and completely reflect the regional characteristics and daily variations at individual sites. Overall, ERA5 overestimates the hourly total solar radiation and direct radiation by approximately 30.87 and 73.95 W/m(2), respectively, whereas it underestimates the diffuse radiation by approximately 43.08 W/m(2). Spatiotemporal differences are found by comparing the errors and time series of different sites. The fact that the accuracy in areas with rainy and cloudy weather is obviously lower indicates that the ERA5 analysis poorly performs when retrieving cloud properties. These conclusions can contribute to guiding the rational use of ERA5 radiation products.