Estimation of downwelling surface longwave radiation for all-weather skies from FengYun-4A geostationary satellite data

Fengyun-4A (FY-4A) is the latest generation of China's geostationary satellite. The Advanced Geosynchronous Radiation Imager (AGRI) onboard FY-4A can provide high-precision, high-frequency observation data, which makes a new possibility for estimating the downwelling surface longwave radiation (DSLR) with high spatial and temporal resolution. This work presents a new method for estimating DSLRs under all-sky conditions using a genetic algorithm-artificial neural network (GA-ANN) algorithm based on brightness temperature (BT) from the FY-4A AGRI infrared channels and near-surface air temperature and dew point temperature from ERA5 reanalysis data. Based on the verification results of two independent observation sites, it is shown that the bias and RMSE are - 4.31 W/m(2) and 35.28 W/m(2), respectively. Compared the CERES SYN all-sky DSLR product with the DSLR estimated by the new method, the bias and RMSE are 0.86 W/m(2) and 26.87 W/m(2), respectively, and the new method has a higher spatial resolution (4 km), which can display more details of spatial variation.