Intraseasonal Synergistic Variation Of The East Asian Upper-level Jet In Winter And Its Impact On Precipitation In Eastern My Country

The East Asian subtropical jet stream and temperate jet stream influence winter in China.It is of great significance to analyze the climate state characteristics of the winter East Asian upper-level jet stream and its influence on winter weather in China,so as to improve the prediction ability of winter weather and climate change in China.Based on ERA-Interim reanalysis data and statistical methods such as filtering and synthetic analysis,this paper analyzes the characteristics of the intraseasonal variation of the East Asian upper-level jet stream(22?N?60?N,70?E?100?E)in winter and upper-level and low-level circulation,and reveals its influence on low-frequency precipitation in eastern China.On this basis,the interannual differences of the intraseasonal collaborative variation intensity of the East Asian upperlevel jet stream in winter are analyzed,and discuss the influence of the thermal effect of the Tibetan Plateau on the intraseasonal collaborative variation intensity.The main conclusions are summarized as follows:(1)It is found that the daily zonal wind of 300 h Pa in winter in East Asia is mainly controlled by biweekly oscillation on the intraseasonal scale.The low-frequency zonal wind at300 h Pa generally propagates eastward,and the low-frequency zonal wind near the polar jet located in the north of the Tibetan Plateau also propagates southward,while the low-frequency zonal wind near the subtropical jet located in the south of the Plateau has no obvious meridional propagation characteristics.With the low-frequency zonal westerly wind moving eastward from the Caspian Sea to over the northwest Pacific Ocean,the polar jet moves eastward and then southeast,and its intensity increases and then decreases.The position of subtropical jet does not change,and the intensity evolution characteristics are opposite to that of temperate jet.The intraseasonal collaborative variation of the upper jet makes the low-frequency characteristics of the upper-level and low-level circulation on the north and south sides of the Tibetan Plateau consistent,and then affects the low-frequency temperature in East Asia and the low-frequency precipitation in eastern China.(2)The low-frequency precipitation has a response to the intraseasonal synergistic change of jet stream,and the significant response area mainly appears in the east of China,moving eastward and disappearing near the western Pacific Ocean.Under the influence of the lowfrequency wind,when the polar jet stream is strong and the subtropical jet stream is weak,the eastern part of China converges in the upper air,and there is strong downdraft in the whole layer,and the ground shows the low-frequency high pressure.The eastern part of China is under the northeast wind,and it is not easy to produce precipitation.When the polar jet is weak and the subtropical jet is strong,the whole layer on the north side of the Tibetan Plateau is consistent with the east wind and on the south side is consistent with the west wind.This state creates high pressure at high altitude in the east of China,and the ground is controlled by low-frequency low pressure,the whole layer upward movement occurs in the east of China.And there is southwest water steam transmission and water vapor convergence,and this makes a positive anomaly of low-frequency precipitation occur in the east of China.(3)There are significant differences in the intensity of the intraseasonal collaborative variation of upper-level jet.In the year with strong intraseasonal change,the polar jet is stronger and the East Asian subtropical jet is weaker,and both jets are northward.In the weak year of intraseasonal collaborative change,there is a low-temperature from the Black Sea to the Bay of Bengal.And in the strong year,there is a high-temperature over the Tibetan Plateau.Further analysis of the winter meridional temperature gradient anomaly,zonal wind anomaly,diabatic heating anomaly and the low-frequency variation standard deviation anomaly of the whole layer temperature shows that the low-frequency variation of the thermal anomaly of the Tibetan Plateau has a significant impact on the temperature field anomaly.Therefore,the thermal effect of the Tibetan Plateau may affect the intraseasonal collaborative variation intensity of the upperlevel jet.