Optimal Meridional Positions of the Tibetan Plateau for Intensifying the Asian Summer Monsoon

Abstract The Tibetan Plateau (TP) exerts significant influences on Earth’s climate, and it is commonly accepted that the plateau enhances the intensity of the Asian summer monsoon (ASM). However, since the TP is located in the subtropics and its climate responses consist of both tropical and extratropical characteristics, a natural question to ask is how the TP would affect the ASM if it were shifted to different latitudes. A series of experiments with a state-of-the-art Earth system model demonstrates that the current location of the TP is not optimal for intensifying the ASM. When the TP is moved southward, the tropical South Asian monsoon (SAM) intensifies, associated with strengthened thermally driven atmospheric circulation, while the subtropical East Asian monsoon (EAM) weakens. When the TP is located in higher-than-current latitudes, on the other hand, the SAM weakens and the EAM intensifies. In particular, when the TP shifts northward by 8° of latitude, the Asian continent witnesses the heaviest summer monsoon rainfall. Changes in the meridional location of the plateau cause substantial differences in atmospheric circulation and water vapor transport, and thus in monsoon rainfall. Significance Statement The existence of the Tibetan Plateau (TP) enhances the Asian summer monsoon; however, the optimal positions of the TP for affecting the monsoon and its various components are unknown. This study shows that the different TP locations exert different influences on the monsoon. When the TP is shifted southward, the South Asian monsoon intensifies while the East and Southeast Asian monsoons weaken. When the TP is shifted northward, the South Asian monsoon weakens constantly while the East and Southeast Asian monsoons strengthen before they become weaker when the plateau is shifted by 12° of latitude. Much of the Asian continent would witness the heaviest monsoon rainfall when the TP is shifted northward by 8° of latitude.