| The Tibetan Plateau (TP) has the spatial heterogeneous climate characteristics due to its huge mountains and complex landform. The Tanggula Mountains running west-east over the TP which induces the significant climate differences between the north (TPN) and the south (TPS) of TP. In addition, the climate differences between the TPN and TPS is relate to the anomalous general circulation in the mid-latitude. Therefore, this paper analysed the rainfall variability and its mechanism in the recent 50 years with the general circulation analysis and the numerical simulation.We used the re-analysis data (e.g., NCEP-I, NCEP-II, ERA-Interim) and the meteorological station data to analyse the variability and its mechanism of rainfall over TP. The EOF, the mutation analysis (Mann-Kendall), the running correlation, and the composite analysis have been used in this study. The main conclusions include:(a) In the past 50 years, summer and winter rainfall shows the anti-phase changing which shows a drier summer and a wetter winter over the TP. A significant anti-phase variation occurs in the early-summer (June) between the TPN and the TPS.(b) The abnormalities of winter planetary wave in Northern Hemisphere (NH) impact on the winter snowfall (WS) over the TP on the inter-decadal scales. In winter, the main general circulation is the "Three Troughs/Ridges in winter" in the NH. Therefore, the variation of the East Asian winter monsoon (WAWM) induces the changing of WS over the TP. The WS over the TP exhibits an upward trend while the strength of WAWM illustrates weakness in 1961-1986. Furthermore, the WS over the TP, the East Asian trough location index (CW) and the Siberian High intensity index (SH) has an abrupt change near 1986. After the abrupt was occurred, the intensity of the winter "three troughs" pattern demonstrates a stronger variation while the amount of WS over the TP is decline.(c) The summer rainfall over TP shows heterogeneous change on spatial scale, especially in June. The June rainfall exhibits an inverse trend between TPS and TPN. The 11-year smoothing mean of June precipitation shows that there are three periods, which are wetter (drier) TPS (TPN) in 1961-1974, wetter (drier) TPS (TPN) in 1994-2004, and drier (wetter) TPS (TPN) in 1981-1991, respectively. The general circulation of the same period indicates that a stronger (weaker) Xinjiang ridge and deeper (shallower) European and American tough are related to more precipitation of June over TPN (TPS) and less ESP over TPS (TPN). The meridian profile (90°-105°E) over TP shows that diabatic heating in June which extends to the middle and upper troposphere have opposite change for 1981-1991 and 1994-2004. Two upward wave trains merge into subtropical jet at the mid-upper troposphere, which are along with the meridian profile of TP (90°-105°E). The strength of south wave train over TP affects the precipitation. The east wind on the south side of TP weak and westerly on the north side of TP accelerate for south more and north less pattern for precipitation. A significant positive correlation between precipitation in June over TPS and the onset date of south Asian monsoon. The earlier onset of south Asian summer monsoon leads to more precipitation in June over TPS. In addition, precipitation in June over TPN is affected by the inter-annual variation of westerlies. The inverse change of precipitation in June over TPS and TPN is due to the effect of thermal forcing over TP and adjustment of general circulations in mid-and high latitudes on the decadal variability.(d) The sensitivity experiments show that if increasing the late-spring season (May) soil moisture in the south of Tibetan Plateau, more summer precipitation will occur over the TP except the central TP. In additional, (1) a weaker general circulation (850 hPa) occurs over the south TP; (2) the Xinjiang Ridge (500 hPa) becomes weaker; (3) enhanced the pressure difference between the north and the south of TP. |
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