Impacts of Local and Remote Sub‐Grid Terrain Solar Radiative Effect on the Meiyu Rainfall Forecast in the Yangtze‐Huaihe River Basin, China

Including the sub‐grid terrain solar radiative effect (STSRE) of East Asia in the convection‐permitting Weather Research and Forecasting model can clearly improve the forecast skill of Meiyu rainfall in the Yangtze‐Huaihe River Basin (YHRB). However, the STSRE of which region mainly leads to the improvement of Meiyu rainfall forecast remains unclear. This study systematically explores the impacts of local and remote STSRE on the Meiyu rainfall forecast, their relative importance, and underlying physical mechanisms. Results show that relative to the remote STSRE of Tibetan Plateau (TP), the local STSRE of YHRB leads to relatively larger improvement of Meiyu rainfall forecast with the root mean square error decreased by 6.24% and Taylor score increased by 2.76%. Further mechanism analysis indicates that the STSRE of the TP weakens the TP heat source, leading to weakening and westward shifting of the South Asian High, which in turn suppresses the divergence in the upper troposphere and the ascending motion over the YHRB and thereafter improves Meiyu rainfall forecast. In contrast, the STSRE of the YHRB decreases surface incident solar radiation and surface thermal conditions, producing a cold anomaly and anticyclonic circulation difference in the lower troposphere over the YHRB. This anticyclonic difference directly weakens southwesterly water vapor transport, thereby reducing the overestimation of Meiyu rainfall. This study highlights the importance of local terrain (rather than the TP) in enhancing Meiyu rainfall forecast accuracy for 3–4 days weather forecasts.