Thermal adaptation of the large-scale circulation to the summer heating over the Tibetan Plateau

The potential vorticity equation is employed to diagnose the variation in t he large-scale atmospheric circulation in July by using the NCAR/NCEP daily reanalysis data from 1986 to 1995. Based on the theory of thermal adaptati on, the schematic diagram of the formation and maintenance of the circulati on over the Tibetan Plateau is revealed in this paper. The result shows tha t near the surface of ground is the positive potential vorticity source pro duced by the increasing diabatic heating with height, which maintains the c yclonic circulation, and that the positive Ertel potential vorticity (PV) s ource is balanced by friction dissipation. On the other hand, in the upper troposphere the negative TV produced by the decreasing diabetic heating wit h height maintains the anticyclone, and it is balanced by the divergence of the negative PV. The Gauss' theorem has been applied to analyze the Ertel potential vorticity flux crossing each of the lateral boundaries of the are a over the Tibetan Plateau. The result shows that the negative PV flux is t ransferred through the eastern and northern boundaries of the area from the Tibetan Plateau region to the outer world. it is evident that the Tibetan Plateau region is an important source of negative vorticity of the atmosphe re.