The Asian summer monsoon affects more than sixty percent of the world's population; understanding its controlling factors is becoming increasingly important due to the expanding human influence on the environment and climate and the need to adapt to global climate change. Various mechanisms have been suggested; however, an overarching paradigm delineating the dominant factors for its generation and strength remains debated. Here we use observation data and numerical experiments to demonstrates that the Asian summer monsoon systems are controlled mainly by thermal forcing whereas large-scale orographically mechanical forcing is not essential: the South Asian monsoon south of 20°N by land–sea thermal contrast, its northern part by the thermal forcing of the Iranian Plateau, and the East Asian monsoon and the eastern part of the South Asian monsoon by the thermal forcing of the Tibetan Plateau.

This paper attempts to provide some new understanding of the mechanical as well as thermal effects of the Tibetan Plateau (TP) on the circulation and climate in Asia through diagnosis and numerical experiments. The air column over the TP descends in winter and ascends in summer and regulates the surface Asian monsoon flow. Sensible heating on the sloping lateral surfaces appears from the authors’ experiments to be the major driving source. The retarding and deflecting effects of the TP in winter generate an asymmetric dipole zonal-deviation circulation, with a large anticyclone gyre to the north and a cyclonic gyre to the south. Such a dipole deviation circulation enhances the cold outbreaks from the north over East Asia, results in a dry climate in south Asia and a moist climate over the Indochina peninsula and south China, and forms the persistent rainfall in early spring (PRES) in south China. In summer the TP heating generates a cyclonic spiral zonal-deviation circulation in the lower troposphere, which converges toward and rises over the TP. It is shown that because the TP is located east of the Eurasian continent, in summertime the meridional winds and vertical motions forced by the Eurasian continental-scale heating and the TP local heating are in phase over the eastern and central parts of the continent. The monsoon in East Asia and the dry climate in middle Asia are therefore intensified.

Monthly mean reanalysis data and numerical experiments based on a climate model are employed to investigate the relative impacts of different types of diabatic heating and their synthetic effects on the formation of the summertime subtropical anticyclones. Results show that the strong land surface sensible heating (SE) on the west and condensation heating (CO) on the east over each continent generate cyclones in the lower layers and anticyclones in the upper layers, whereas radiative cooling over oceans generates the lower-layer anticyclone and upper-layer cyclone circulations. Such circulation patterns are interpreted in terms of the atmospheric adaptation to diabatic heating through a potential vorticity–potential temperature view. A Sverdrup balance is used to explain the zonally asymmetric configuration of the surface subtropical anticyclones. The strong deep CO that is maximized in the upper troposphere over the eastern continent and the adjacent ocean is accompanied by upper-tropospheric eq... Abstract Monthly mean reanalysis data and numerical experiments based on a climate model are employed to investigate the relative impacts of different types of diabatic heating and their synthetic effects on the formation of the summertime subtropical anticyclones. Results show that the strong land surface sensible heating (SE) on the west and condensation heating (CO) on the east over each continent generate cyclones in the lower layers and anticyclones in the upper layers, whereas radiative cooling over oceans generates the lower-layer anticyclone and upper-layer cyclone circulations. Such circulation patterns are interpreted in terms of the atmospheric adaptation to diabatic heating through a potential vorticity–potential temperature view. A Sverdrup balance is used to explain the zonally asymmetric configuration of the surface subtropical anticyclones. The strong deep CO that is maximized in the upper troposphere over the eastern continent and the adjacent ocean is accompanied by upper-tropospheric eq...