Revealing Key Factor in Cloud Radiation Processes Affecting Global Horizontal Irradiance in WRF‐Solar in China

Abstract Precise forecasting of global horizontal irradiance (GHI) is crucial for weather forecasting and solar energy production. The Weather Research and Forecasting Solar (WRF‐Solar) model, especially its sub‐grid cloud scheme (CLD), plays a key role in GHI prediction. This study mainly uses various CLD schemes (icloud option in different WRF‐Solar version, CLD1 v4.4 and CLD3 v3.8, v4.2, and v4.4) to explore the key factors in cloud radiation processes and causes of deviations that affect GHI in China. Results illustrate that WRF‐Solar generally overestimates GHI, with poorer simulations in Henan and southwestern China. The impact on GHI is minimized when the cloud fraction (CF) is the only influencing factor (default CLD) at 3 km horizontal resolution. There will be a compensating effect of CF and cloud condensate content for GHI feedback, but under extremely low CF, its impact exceeds the compensation from increased cloud condensate content. Employing the default climatological effective particle radius of clouds in the RRTMG radiation scheme would improve GHI prediction, especially for Henan Province. All CLD3 versions have enhanced simulations on GHI compared to CLD1 due to the incremental adjustments in cloud condensate content, with CLD3 v3.8 (CLD3_38) showing the best performance, which would reduce MB by 54.8% and RMSE by 11.1% at 13:00 across China. Furthermore, comparing CLD3_38 with Fengyun4A shows WRF‐Solar overestimates high clouds, causing discrepancies in cloud phase representation, especially in northwest China, while poor GHI simulation in southwestern China is linked to inadequate low and medium cloud representation.