Seasonal Difference in the Impact of Sub‐Grid Turbulent Orographic Form Drag Scheme on the Simulations of Winds and Precipitation Over China

Abstract

This study systematically evaluates the influence of the sub‐grid turbulent orographic form drag (STOFD) scheme on the performance of the Regional Climate Model Version 4 in simulating 10 m wind and precipitation over China across seasons and investigates underlying mechanisms. Results demonstrate that the improvement of 10 m wind simulation across China induced by STOFD scheme is the most pronounced in winter among all seasons, reducing root mean square error (RMSE) by 27.72% and increasing Taylor score by 46.09% for wind speed, with improvement degree positively correlated with micro‐scale terrain complexity. The effects of STOFD scheme on precipitation simulations also vary seasonally. Specifically, adopting STOFD scheme most effectively reduces precipitation overestimation over the Tibetan Plateau in winter among all seasons, with RMSE reduced by 9.69%. The greatest improvements in precipitation simulations over the Southeastern and Northeastern China occur in summer among all seasons, with RMSE reductions of 6.45% and 33.11%, respectively. Mechanistically, STOFD impedes westerlies, generating southeasterly wind differences that trigger secondary meridional circulation and pressure differences, enhancing westerlies on both sides of the southeasterly wind differences and inducing cyclonic (anticyclonic) differences over the Southeastern (Northeastern) China. Seasonal variations in the intensity and position of background westerlies modulate the magnitude and distribution of STOFD‐induced 10 m wind simulation improvements, thereby driving the seasonality of impacts on regional circulation and water vapor transport, shaping clear seasonal differences in improvements of precipitation simulations. This study reveals seasonality in the effects of STOFD scheme, offering crucial insights for model development.