The Drying Tendency in the Southern Tibetan Plateau during Recent Past Decades

The Tibetan Plateau (TP) exerts a significant impact on the weather and climate over many places of the world through both mechanical and thermal-dynamical effects. In summer, the major rainfall of the TP occurs over the southern slope, and the associated atmospheric latent heating dominates the total diabatic heating of TP. It is found that there is a drying tendency in the southern TP (STP) during recent past decades, especially in July to September (JAS). Based on the decompose of moisture transport, it is indicated that the associated weakened dynamic condition is responsible for the decreased rainfall in STP, which is further corresponding with the northward shift of the westerly jet (WJ) in recent decades. On the one hand, the northward shift of WJ can weaken the westerly wind over the STP, and reduce the westward moisture transport along the Himalayas. On the other hand, the northward shift of WJ would reduce the upper-level anticyclone over the STP, and weaken the upper-level divergence. There is a significant weakened trend of divergence over the STP, corresponding with a trend of vertical sinking motion. Overall, the northward shift of WJ induces unfavourable dynamic conditions for the STP rainfall in recent past decades.