The Spacial Structure Of Asian Jet Stream And Its Relation With Winter Climate In China

Based on NCEP/NCAR monthly reanalysis data of wind and height, the sea surface temperature(SST) dataset provided by the Met Office Hadley Centre, the surface heating field data of Tibetan Plateau and daily observed data of542stations in China, by using the empirical orthogonal functions(EOF), the singular value decomposition(SVD), corelation analysis and composite methods, the spatial structure of Asian jet stream and seasonal variation of vertical motions below it are investigated, as well as the relationship between configuration of upper-tropospheric jet activity and winter monsoon and their impact on distribution of winter climate in China.It is also discussed the respond by Asian jet stream to the tropical SST and anomaly surface heating field of Tibetan Plateau.The results show that subtropical jet is divided into tubular and irregular structures.The jet’s volume becomes largest in winter, and its vertical thickness ranges from500hPa to100hPa. In summer, the jet was just visible at200hPa and its volume was smallest.The jet tube runs from southwest to northeast in autumn, winter, and spring, but from west to east in summer. The meridional movement of mean axes,which represents the greatest wind speed from500hPa to100hPa, is not synchronous.The wind axes at low levels are always north of the high ones in spring and autumn.The vertical motions below each part of the Asian jet are different and vary seasonally. The descending motion center always occur at the south of jet stream over West Asia all the year around, while over the East Asia, there is descending motion center occur at the north of jet stream in winter but ascending motion in summer. Apart from the mean meridional circulation, the vertical motion over the Plateau is significantly influenced by the heating of Plateau either. In the winter of Northern Hemisphere, the chief modes of Asian jet stream are meridional movement and opposite variation between subtropical jet and temperate jet, meanwhile the Middle East jet varies oppositely from the East Asian jet.It is indicated that when intensity of the subtropical jet stream from the Tibetan Plateau to China east coast is increased(decreased), while of the temperate jet stream in the middle-high latitude is decreased(increased), temperature in greater part of China tend to be lower(higher). If intensity of Middle East jet is increased(decreased), East Asian subtropical jet stream move towards south(north) and wind of southeastern temperate jet is weak(strong), temperature in southwest China is lower(higher) while in northeast is higher(lower), there is more(less) precipitation in Eastern China. Combined with variation of horizontal wind components, the westerly anomaly over subtropical regions and easterly one over temperate,which strengthen the East Asian trough and weaken the high pressure on the Tibetan Plateau, leading to stronger East Asian monsoon and weaker Plateau monsoon, result in cold air in high latitude moving toward south. The velocity gradient of zonal wind between subtropical belt and temperate zone appear to reinforce the confluence of cold air and warm air at low level.Correlation matrix shows that East Asian monsoon index(EAMI) and Plateau monsoon index (PMI) have significant negative correlation in winter. During a period with abnormal winter monsoon, if intensity of subtropical jet is strong while temperate jet is weak, the cold air would be sucked to South China, leading to reduce temperature and there are less rainfall in China.Conversely, the warm air would be sucked to North China, then temperature rise and tend to be more precipitation in China.It is found that the Asia jet stream move toward south as tropical east Indian ocean and middle and east Pacific ocean sea surface temperature(SST) is anomaly warm, while tropical west Pacific ocean SST is cold in winter. If tropical Indian ocean SST of the whole basin is anomaly warm in autumn,then the jet stream over Middle-East and Tibetan Plateau would be strengthen. The variation of velocity of jet stream northwest to Tibetan Plateau is related to the surface heating fields over Plateau.