Does the modern‐era retrospective analysis for research and applications‐2 aerosol reanalysis introduce an improvement in the simulation of surface solar radiation over China?

Surface incident solar radiation ( R s ) is a key parameter of energy and water cycles of the Earth. Reanalyses represent important sources of information on R s . However, reanalyses R s may have important bias due to their imperfect parameterizations and input errors of cloud and aerosol. NASA's Global Modelling and Assimilation Office has recently released Version 2 of the Modern‐Era Retrospective Analysis for Research and Applications (MERRA2), which incorporates a reanalysis of atmospheric optical depth for the first time. In this study, we evaluate R s from MERRA2 and its predecessor (MERRA) in China from 1980 to 2014. We first compare three possible reference data sources: (a) observed R s at 122 stations, (b) satellite retrievals of R s and (c) R s values derived from sunshine durations measured at 2,400 weather stations. We find sunshine duration derived R s is a reliable reference and use it to evaluate MERRA and MERRA2. Our results show that both MERRA and MERRA2 have a high mean bias of 38.63 and 43.86 W/m 2 over China due to their underestimation of cloud fraction, which is greater in southern China. MERRA2 displays improved capability in reproducing monthly and annual variability, and national mean trend of R s . MERRA overestimates the trend of R s by 3.23 W/m 2 in eastern China. MERRA2 reduced this trend bias over the North China Plain likely due to its aerosol assimilation. However, MERRA2 show a negative bias in trend of R s (−3.44 W/m 2 ) in the south China likely due to its overestimation of atmospheric aerosols loading and aerosol‐cloud interaction. The results provide guidance for future development of reanalysis and its scientific applications for ecological and hydrological models.