Applicability Evaluation of Himawari-9 Downward Surface Shortwave Radiation (DSSR) Product under Complex Weather Conditions: A Case Study of Guangxi

The Advanced Himawari Imager (AHI) aboard Himawari-8/9 can provide downward surface shortwave radiation (DSSR) with 5 km and a high temporal resolution of 10 min. To evaluate its applicability under complex meteorological and topographic conditions, this study systematically assesses the overall quality of the Himawari-9 DSSR product in Guangxi region and its performance under different cloud and aerosol conditions, based on ground-observed observations from photovoltaic and meteorological stations in 2023. The overall comparison of hourly AHI DSSR and ground DSSR shows a high correlation coefficient (R = 0.85); however, there is also a large bias (RPE (relative prediction error) = 46.71%, RMSE (root mean square error) = 162.99 W/m2). Errors are larger in spring and summer, and spatially, errors are significantly higher in the hilly and mountainous areas of northwestern Guangxi compared to the flatter southern and central regions. Satellite retrieval accuracy degrades markedly as cloud cover and aerosol level intensify, with the correlation coefficients dipping from 0.90 (clear sky) to the lowest values of 0.11 (COD (cloud optical depth) > 50) and slightly decreasing from 0.84 (0 ≤ AOD (aerosol optical depth) ≤ 0.1) to 0.79 (AOD >2), respectively. These findings reveal critical limitations of satellite DSSR products under specific atmospheric conditions, providing essential guidance for photovoltaic resource assessment and power forecasting applications in Guangxi. It also serves as an important reference for the evaluation and application of satellite-derived surface radiation products at the national scale.