Huang Yang, Li Cuina, Wang Xiang, Dai Tie, Shi Rui, Sun Hao
A multi-temporal and spatial scale evaluation of Himawari-9 shortwave radiation data is conducted using hourly total radiation measurements from 136 ground-based radiation stations across China in 2023. The results show that： 1） On a national average diurnal variation, during 08:00—18:00, the correlation coefficient （Corr） between the Himawari-9 shortwave radiation data and the ground-based radiation data exceeds 0.85, displaying a unimodal distribution. The highest correlation occurs at 09:00 and 10:00, both reaching 0.95, while the lowest occurs at 19:00, with a value of 0.77. The root mean square error （RMSE） also shows a unimodal pattern, with the highest RMSE at 15:00, reaching 119.19 W/m², and the lowest at 08:00, only reaching 49.73 W/m². The bias exhibits a bimodal distribution, with peaks at 10:00 and 15:00. The highest bias occurs at 15:00, reaching 49.63 W/m², and at 10:00 it is 18.46 W/m². The lowest bias is observed at 19:00, with a value of 0.04 W/m². 2） On a national average annual variation, the correlation coefficient displays a bimodal distribution, but there is little variation between months. The two peak values appear in April and October, both at 0.96. The RMSE shows a unimodal distribution, peaking in summer （July-August） with values exceeding 100 W/m², while lower values are observed in autumn and winter. The bias follows a unimodal distribution, with the highest values in spring. In March and April, the bias exceeds 25 W/m², and the lowest value occurs in December, at 6.68 W/m². 3） Spatially, higher correlation values are concentrated in central and eastern China, while lower values are found at some stations in northern and plateau regions. Central and eastern regions are low RMSE areas, where Himawari-9 shortwave radiation data exceeds ground-based radiation data, while western, northern, and plateau regions are high RMSE areas, where Himawari-9 shortwave radiation data is lower than ground-based radiation data. 4） Further analysis of the impact of altitude on the quality of Himawari-9 shortwave radiation data shows that, overall, as altitude increases, the correlation coefficient decreases, and RMSE increases. In regions below 2000 m, Himawari-9 shortwave radiation data generally exceeds ground-based measurements, while in regions above 2000 m, Himawari-9 shortwave radiation data tends to overestimate low irradiance and underestimate high irradiance. Grouping by satellite zenith angle reveals that, in low- to mid-altitude regions, RMSE shows a single-valley distribution. At zenith angles between 20° and 25°, RMSE is the lowest. When the zenith angle is below 20°, the bias is negative, but as the zenith angle increases, the bias becomes positive and gradually increases. In high-altitude regions, there is little difference when the zenith angle is below 35°, but when it exceeds 35°, the correlation coefficient is the lowest, and RMSE is the highest.
