Long-term evolution of clear sky surface solar radiation and its driving factors over East Asia

This study evaluated the performance of clear sky surface solar radiation (SSR) and its long-term evolution mechanism in the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) in East Asia. The results revealed that although MERRA-2 overestimated the clearness index and clear sky SSR, the reanalysis performed well in northwestern, northern, northeastern, and central East Asia. From 1980 to 2019, clear sky SSRs decreased significantly in most areas. Aerosols play a dominant role in the annual variation of clear sky SSR rather than water vapor. In northwestern East Asia, owing to the influence of the increase in aerosol optical depth (AOD), the clear sky SSR showed a strong downward trend during 1993-2013. After 2007, the increase in water vapor played an important role in the weakening of the clear sky SSR. In northern, northeastern, and central East Asia, clear sky SSRs ushered in a brightening stage at the beginning of the 21st century because of the reduction in AOD. The magnitude of the change in Central East Asia is even more pronounced. In the Tarim Basin and northwestern India, dust plays an important role in the variation of clear sky SSR, whereas anthropogenic aerosols drive clear sky SSR in highly industrialized regions.