A high-quality hourly, daily and monthly solar irradiance dataset in China during 1981–2014 based on MERRA-2 Reanalysis products

Abstract. Solar irradiance (SI) is the main driving factor contributing to climate change and energy balance between the land and atmosphere. High-quality records of global solar irradiance (GHI), direct normal irradiance (DNI) and diffuse solar irradiance (DIF) are of vital importance for solar applications, but the solar radiation observations are sparse around the world. As an alternative, numerous SI reanalysis data in grid format have been developed in regional and global scales. Among them, the MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) products could provide high quality SI records with acceptable accuracy and long temporal ranges. This study attempted to improve the accuracy of GHI records derived from MERRA-2 products, and to generate grid DNI and DIF datasets for all-sky conditions over mainland China during 1981–2014, based on the REST2 model and cloud transmittance estimates combining sunshine observations. The results indicate that the estimated GHI values (GHInew) show higher agreements with GHI measurement at 17 CMA (China meteorological administrations) stations than that for the GHI records derived from MERRA-2 products (MERRA-2 GHI). Then, grid GHI, DNI and DIF datasets (0.50° (lat) *0.625° (lon)) throughout China were constructed. The results indicated that the MERRA-2 GHI records may overestimate the GHI values over mainland China. Generally, the GHI and DNI values gradually decreased during 1981-2014, however, DIF values gradually increased from 1981 to 2014, especially in 1992 (DIF = 90.914 W m⁻², anomaly DIF value = 15.544 W m⁻²). The Qinghai Tibetan Plateau has always been an area with the highest GHI, the highest DNI and the lowest DIF values, whereas the Sichuan Basin has always been an area with the lowest GHI, the lowest DNI and the highest DIF values. The grid GHI, DNI and DIF dataset generated in this study can assist in numerous solar studies and applications. We provide these solar irradiance data in publicly available repository: https://doi.org/10.6084/m9.figshare.10026563 (Qin, W. et al., 2019).