资源环境科技发展态势分析平台

Recent studies have demonstrated that mechanical effects have a greater contribution to the East Asian summer monsoon (EASM) than thermodynamical effects. However, a theoretical basis for the underlying dynamical mechanism has not been elucidated. The present study shows that topographically forced barotropic Rossby wave theory well explains the seasonal evolution of the monsoonal precipitation and its amplitude and peak location. The subtropical zonal wind impinging on the Tibetan Plateau is a key factor, and the resulting downstream cyclonic and anticyclonic circulation anomalies form a peak zonal geopotential height gradient in between, leading to the development of the meridional wind and the accompanying moisture transport to the EASM region. As the season approaches the summer monsoon period, the peak geopotential height gradient – thus the monsoonal rainband – shifts to the west from the western North Pacific to East Asia. The findings in this study can be applied to subtropical monsoons worldwide.