Variation of the Tibetan Plateau summer monsoon under the background of global warming and its impact on the climate in southwestern China

The new Tibetan Plateau (TP) summer monsoon indices were defined according to the vorticity characteristics at 600 hPa over the TP, and their impacts on the southwestern China climate had been analyzed by using the NCEP/NCAR reanalysis data from 1951 to 2012 and the surface meteorological data at 116 stations in southwestern China from 1960 to 2012 under the background of global warming. The intensification of the TP summer monsoon has reached the peak in the late 1990s, consistent with the global warming trend, but the locations are different from each other. There are two indices, the intensity and the position of the central longitude of the TP summer monsoon, which have significant effects on the southwestern China climate change. A stronger TP summer monsoon is favorable for more moisture convergence, more cloudy and rainy days, less sunshine, weaker evaporation and smaller diurnal temperature range in southwestern China. Moreover, the meteorological elements vary more significantly in the Sichuan-Chongqing region with the deep updraft development than in the Yunnan-Guizhou region with the ascending flow limited to below 600 hPa. When the central longitude moves to the east, the whole southwestern China is controlled by the abnormal sinking motion, which contributes to a higher temperature. There appears abnormal strong moisture divergence in the middle-western part of Sichuan, Guizhou, and Guangxi, which result in higher temperature, lower humidity and less rainfall over the above regions. Since the 21st century, the shrinking intensity and eastward-moving of the TP summer monsoon conspire to cause the drying trend of southwestern China. The new TP summer monsoon indices can not only reflect the monsoon circulation on the TP, but also have a good relationship with the climate change in southwestern China. This research provides a theoretical foundation for the drought-flood prediction of southwestern China.