The Role of Thermal Pumping Action in the Tibetan Plateau Summer Monsoon and its impact on the South Asian High and East Asian Atmospheric Circulation

The Tibetan Plateau (TP) is well known for its unique sensible heat driven air-pump in summer, characterized by low-level convergence and upper-level divergence. This study defines a Pumping Plateau Monsoon Index (PPMI) based on the divergence difference between 200 hPa and 600 hPa derived from NCEP-DOE Reanalysis-2 data. The PPMI characterizes the intensity of the TP thermal pumping effect and its associated three-dimensional circulation structure. The PPMI also shows significant correlations with the TP heat source, the east-west displacement of the South Asian High (SAH), and downstream East Asian Summer Monsoon (EASM) precipitation. During weak Tibetan Plateau Summer Monsoon (TPSM) years, an anomalous anticyclonic circulation is induced over the Iranian Plateau, shifting the SAH westward toward the Iranian High. Meanwhile, a reversal of the meridional gradient of potential vorticity leads to a bifurcation of the Rossby wave train, thereby suppressing its eastward propagation. During strong TPSM years, an anomalous cyclone-anticyclone-cyclone-anticyclone circulation pattern is correspondingly induced from the Iranian Plateau, the TP, Northeast China, to the Northwest Pacific. This pattern enhances the downstream propagation of quasi-stationary Rossby wave train and changes the upper-level circulation over the EASM oceanic region, thus inducing anomalous ascent that promotes precipitation development and latent heat release. These processes further accelerate the establishment of the EASM and deepen the East Asian Trough. These results clearly elucidate the teleconnection mechanism through which TPSM modulates the onset of EASM, providing a new dynamical perspective for forecasting EASM onset.