Improvement of ERA5 over ERA-Interim in Simulating Surface Incident Solar Radiation throughout China

Surface incident solar radiation (R-s) is important for providing essential information on climate change. Existing studies have shown that the R-s values from current reanalyses are significantly overestimated throughout China. The European Centre for Medium-Range Weather Forecasts (ECMWF) recently released the fifth generation of atmospheric reanalysis (i.e., ERA5) with a much higher spatiotemporal resolution and a major upgrade compared to its predecessor, ERA-Interim. This study is to verify whether ERA5 can improve the R-s simulation using sunshine duration-derived R-s values at similar to 2200 stations over China from 1979 to 2014 as reference data. Compared with the observed multiyear national mean, the R-s overestimation is reduced from 15.88 W m(-2) in ERA-Interim to 10.07 W m(-2) in ERA5. From 1979 to 1993, ERA-Interim (-1.99 W m(-2) decade(-1); p < 0.05) and ERA5 (-2.42 W m(-2) decade(-1); p < 0.05) estimates of R-s in China continued to decrease and the decline of the latter is closer to the observed. After 1993, they both show a strong brightening (i.e., 2.26 W m(-2) decade(-1) in ERA-Interim and 1.49 W m(-2) decade(-1) in ERA5) but observations show a nonsignificant increase by 0.30 W m(-2) decade(-1). Due to the improvement of total cloud cover (TCC) simulation by ERA5, its R-s trend bias induced by the TCC trend bias is smaller than that in ERA-Interim. In addition, the reason why the simulation trend in ERA5 remains biased might be that ERA5 still ignores aerosol changes on interannual or decadal time scales. Therefore, subsequent reanalysis products still need to improve their simulation of clouds, water vapor, and aerosol, especially in aerosol direct and indirect effects on R-s.

Automated summary

This study verified the improvement of surface incident solar radiation (R-s) simulation in China by the European Centre for Medium-Range Weather Forecasts' fifth generation reanalysis (ERA5) compared to its predecessor, ERA-Interim. While ERA5 showed reduced overestimation of R-s values, it still exhibits bias in simulation trends due to ignoring aerosol changes on interannual or decadal time scales. Subsequent reanalysis products need to focus on improving simulation of clouds, water vapor, and aerosols, particularly in understanding aerosol effects on R-s.