A. M. Duan G. X. Wu Role of the Tibetan Plateau thermal forcing in the summer climate patterns over subtropical Asia Received: 27 May 2004 / Accepted: 20 October 2004 / Published online: 13 May 2005 Ó Springer-Verlag 2005 Abstract The mechanism of the Tibetan Plateau (TP) thermal forcing in influencing the summer climate pat- terns over subtropical Asia is investigated by means of NCEP/NCAR reanalysis diagnosis. Results show that since the TP is a huge elevated heating source with the strongest heating in the surface layers in summer, the thermal adaptation results in a shallow cyclonic circu- lation near the surface and a deep anticyclonic circula- tion above it. According to the steady barotropic vorticity equation for large scales, airflow must converge in the lower layers and diverge in the higher layers over the eastern side of the TP. However, the western side of the TP is characterized by a reversed structure, i.e., divergence in lower layers but convergence in higher layers. Hence, pumping and sucking processes bring in upward and downward movement over the east and west sides of the TP, respectively. Such a circulation is embedded in the large-scale circulation that is forced by the Eurasian continental heating. Because the TP to- gether with Iran Plateau are located at the central and eastern parts of the continent, and, because the orog- raphy-induced circulation is in phase with the conti- nental scale circulation, the role of the TP thermal forcing is to intensify the East Asian monsoon to its east and the dry and hot desert climate in mid-Asia to its west. The summertime thermal forcing of the Rockies and Andes can generate similar circulations along the two subtopics as the TP does since they are located near the western coasts. But, the lower troposphere poleward flow that is induced by orographic thermal forcing does not coincide with the poleward flows over the eastern coastal region that is induced by continental heating and the monsoon rainfall in North and South America is not as strong as in East Asia. However, the equatorward flow and the associated subsidence induced by the two mountain ranges along the western coasts of both North and South America are in phase with those induced by continental heating. These contribute to the formation of the stable low stratus clouds and strong long-wave radiative cooling over the eastern subtropical Pacific regions just off the western coast of the continent. 1 Introduction It is well known that a large-scale mountain exerts sig- nificant influence on the atmospheric circulation through its mechanical and thermodynamical effects. Pioneering observation diagnoses such as Yin (1949), Yeh (1950), Flohn (1957), Yeh et al. (1957), Murakami (1958), Koteswaram (1958), and Staff Members of Academia Sinica (1957) have revealed the features of circulation and heating in different seasons over the Tibetan Plateau (TP) and discussed their possible con- nection with the mechanical and thermal aspects of the TP forcing. These papers, accompanied by theoretical and numerical modeling studies (e.g., see Charney and Eliassen 1949; Bolin 1950; Hoskins and Karoly 1981; Wu 1984; Rodwell and Hoskins 2001) have revealed the important role of mechanical forcing in the formation of atmospheric circulation in winter. However, the circu- lation in the summer subtropics seems to be more related to thermal forcing, and its formation mechanism is more complicated compared to other latitudes (Hoskins 1987; Rodwell and Hoskins 2001) . According to the results of numerical simulation and data analysis, Rodwell and Hoskins (2001) argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems, each involving monsoon rains, a low-level poleward jet, a subtropical anticyclone to the east, and descent and equatorward flow to the west. A local ‘‘di- abatic enhancement’’, which is produced by interaction A. M. Duan G. X. Wu (&) State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, 100029, China E-mail: gxwu@lasg.iap.ac.cn Climate Dynamics (2005) 24: 793–807 DOI 10.1007/s00382-004-0488-8