Drying Tendency over the Southern Tibetan Plateau in 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 its southern slope, and the associated atmospheric latent heating dominates the total diabatic heating of TP. It is found that there was a drying tendency over the southern TP (STP) in recent past decades, especially in July to September (JAS). Based on the data analyses, it is indicated that the drying STP is mainly attributed to the internal variability of the atmosphere, characterized by the upper level signature of a circumglobal wave train (CGT) extending from the North Pacific to Eurasia. The long-term change of CGT during the past decades induces a significant anticyclonic anomaly over the north of TP, which is further corresponding with the northward shift of the westerly jet (WJ) in recent decades. The northward shift of WJ can weaken the westerly wind over the STP, and then reduce the westward moisture transport along the Himalayas. More importantly, 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.