Roles of tropical and subtropical land_sea distribution and the Qinghai_Xizang Plateau in the formation of the Asian summer monsoon
热带、副热带海陆分布与青藏高原在亚洲夏季风形成中的作用

Roles of tropical land-sea distribution and the Qinghai-Xizang Plateau in the formation of the Asian monsoon are examined through a series of idealized numerical experiments.Results show that the existence and geometric shape of land-sea distribution crucially affect the Asian summer monsoon.In an aqua-planet case,no monsoon is observed.In an experiment in which only the subtropical Eurasian landmass exists while the South Asian and African tropical lands are missing,there is a weak summer monsoon over its southeastern corner,but no evident cross-equatorial flow in summer and no summer monsoon over India,the Bay of Bengal (BOB),or the South China Sea(SCS).The existence of tropical lands such as the Indochina Peninsula,the Indian Peninsula and the African continent,induces cross-equatorial flows and strong low-level southwesterlies over the tropical regions,leading to the formation of the Asian summer monsoon over India,the BOB,and the SCS.The extension of the subtropical continent into the tropics greatly enhances the summer convective rainfall over the subtropical land.The Qinghai-Xizang Plateau works the East Asian monsoon as an amplifier,makes it strengthen and develop northward.However,the South Asian monsoon becomes weak and shrinks southward under effects of the Qinghai-Xizang Plateau.