On the basis of National Centers for Environmental Prediction /National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, and through artificial identification and comparison of weather maps, the climatic characteristics of the Tibetan Plateau Vortex (TPV) in summers of 1981 to 2010 are analyzed in this paper, and the characteristics of the atmospheric circulation and low-frequency component field are comparative studied in high-and low-frequency years of the TPV, respectively. The main results are summarized in the following points:
(1) During the past 30 years, 32 TPVs were generated over the Tibetan Plateau in summer, and the occurrence frequency of the TPV presents an obvious increasing trend and a strong interannual variability. The vortex frequency appears as significant mutations in 2000 and 2005, shifts from an increasing trend to decreasing trend in 2002, and converts into a growing trend in 2005. Moreover, the vortex frequency has significant potential for quasi-periodic oscillations to occur in periods of approximately 5, 9, and 15 years. The TPV frequency generated in June shows a decreasing trend that increase in July and August.
(2) The generating sources of the TPV in summer appear mainly in the regions of Shuanghu and Nagqu in Tibet and Zarenkewu in Qinghai in the central, western, and eastern plateau respectively accounting for 50.8%, 27.0%, and 22.2% of the total. The TPVs in summer generated in June, July, and August respectively account for 44.7%, 29.9%, and 25.4% of the total. The warm TPVs in summer make up the vast majority, accounting for 90.7% of the total. About 1.3 TPVs could develop strongly and move out of the plateau every summer during the past 30 years, which produce heavy rainfall in a wide range of downstream areas. The TPVs moving out of the Tibetan Plateau with east,northeast, and southeast shifting accounted for 56.4%,20.1%, and 20.5%,respectively.
(3) During the high-incidence years of TPV, the atmospheric circulation and low-frequency components of the atmospheric circulation at low levels show strong horizontal convergence and southerly airstream, and the Tibetan high is stronger than the climatology within the main body of the plateau at high levels. The opposite occurs in low-incidence years of the TPV. The configuration of cyclones over the Iranian Plateau, a trough over the Tibetan Plateau, and an anticyclone in the south side of the plateau have important roles in the occurrence of the TPV.