The Analysis Of Characteristic Of A Couple Of Vortexes On The East Side Of Tibetan Plateau And Their Impact On The Weather And Climate In China

Affected by Tibetan Plateau terrain, the lower-level west wind is split on the east side of plateau and forced to flow around it. There are two branches of the westerly, one flow to the south of the plateau forming a positive vorticity belt, and the other to the south of the plateau forming a negative belt. They converge on the east side of the plateau. Utilizing the NCEP/NCAR reanalysis data from 1951 to 2004, we discovered that the two vorticity belts were most obvious on the 700hPa, and there were a couple of vortexes on the east of the plateau all the year round. According to the monthly position and intensity of the vortexes, a Detouring Flow Index (DFI) from winter to spring is defined as the difference between the average vorticity of the positive vortex and the negative one, quantitatively characterized the Function of Detouring Flow around Tibetan Plateau (FDFTP). In addition, we study its impact on the weather and climate in China. The results demonstrated that:Ⅰ.From 1951 to 2004, the FDFTP is stronger in spring than that in winter in 2/3 years. Inter-decadal variation of the DFI is dominant in winter, and the DFI is obviously enhanced in last 50 years. Both inter-decadal change and annual change of the DFI are not significant in spring.Ⅱ. Both in winter and spring, DFI can characterize the intensity of the couple of vortexes and the FDFTP well. Effects of FDFTP on the temperature in winter have two different characteristics: on inter-annual timescale, enhanced FDFTP is favorable to induce low temperature in northeast China and northern part of Xinjiang Province; on inter-decadal timescale, enhanced FDFTP is favorable to increase temperature in most area of China in winter.Ⅲ. In spring, enhanced FDFTP is favorable to induce low temperature in northeast China and northern part of Xinjiang Province, it is also favorable to transport warm and wet current to southern China, induced high temperature there. The meeting of cold and warm air near 31°N may cause heavy rain in the Yangtze-Huaihe region and it is shown that enhanced FDFTP in spring relates to high temperature in mid and lower reaches of Yangtze River and Huaihe region.Ⅳ. From winter to spring, intensity of the westerly belt in middle latitude in Asia is one of important effect factors to the inter-decadal variability and annual variability of the FDFTP.Ⅴ. From winter to spring, the difference of the visible heat sources in the whole atmospheric column in south and north of Asia in middle latitude is another important effect factors to the FDFTP, especially for the inter-decadal variability and annual variability of the FDFTP in spring.