An Analysis Of The Rossby Wave Propagation Along The Asian Subtropical Westerly Jet In Summer And Its Relationship With Precipitation In My Country

By using the daily reanalysis data of National Centers for Environmental Prediction-National Center for Atmospheric Research(NCEP)with a resolution of2.5°×2.5°and daily precipitation data at 20BT(Beijing time)from Chinese meteorological stations in the summer of 1950-2015(June-August),based on the method of vorticity source equation,the perturbation kinetic energy equation and Eliassen-Palm flux,the wave sources,energy propagation of Rossby wave activities along the Asian Subtropical Westerly Jet Stream(ASWJ)in summer and its relationship with precipitation and anomalies in China are analyzed and studied.The results show that:(1)The spatial distribution and climatological variations of the westerly jet in the Asian subtropical region are analyzed.It is found that there are three large wind velocity centers in the summer climatic 200 hPa zonal wind field along the 40°N westerly jet axis in the Asian subtropical westerly jet,which are located near the Caspian Sea at 50 °E,the northern Xinjiang region with 80°E-105°E,and Japan at135°E-150°E and its east ocean,showing a quasi-stationary Rossby wave pattern along the zonal three-wave pattern along the ASWJ.The origin of quasi-stationary Rossby waves along ASWJ is mainly in the Mediterranean region,where the waves are excited and propagated eastward along the jet current.During the eastward propagation process,the energy is dissipated and the propagation velocity decreases gradually as a whole.The convergence and divergence centers of wave flux are alternately distributed along the subtropical westerly jet,showing a "+-+-+" long wave-scale three-wave train structure in the zonal direction,the wave-current interaction is the dynamic mechanism of the alternating variation of westerly intensity in ASWJ.(2)The correlation between the critical region of wave interaction flux divergence and the whole wave interaction flux divergence field is analyzed.It is shown that the convergence and divergence center of wave interaction flux alternately distributed along the jet current is a different part of the same Rossby wave train.The variation of the wave action flux divergence at the source has a significant effect on the convergence and divergence center strength of the lower reaches of the jet,and also affects the intensity of the zonal wind downstream of the subtropical westerly jet,which reflects the downstream dispersion effect of the Rossby wave energy along the subtropical westerly jet.The variation of the average perturbation kinetic energyintensity at the wave source is closely related to the variation of the wave action flux divergence and the jet center intensity in the downstream region.When the upstream Rossby wave average perturbation kinetic energy deviation is strong,the wave action flux divergence is strong,the central strength of the jet flow in the downstream area is relatively strong.(3)The relationship between the Rossby wave propagation along the subtropical westerly jet and precipitation in China in summer is analyzed.The wave source flux divergence indices WFD-I and WFC-II located in the wave source and in the upper reaches of the Qinghai-Tibet Plateau to the Loess Plateau in China are more correlated with precipitation in the south and north of China.Statistical analysis in the summer of 56 years shows that when the WFD-I is positive anomaly year,the proportion of precipitation in the key areas of the south is 62.5%,and when it is negative anomaly year,the proportion of precipitation in the key areas of the north is80%.When WFC-II is positive anomaly year,the proportion of precipitation in the key areas of the south is 66.7%,and when it is negative anomaly year,the proportion of precipitates in the key areas in the north is 81.8%.(4)Studying the circulation cause of precipitation anomaly in China caused by the wave activity flux divergence index WFD-I anomalous years at wave source in summer,it is found that when WFD-I is positive anomalous year,the vorticity source region is southward than the climatological state as a whole,and the disturbance energy of Rossby wave in the source region is stronger,the excited Rossby wave is stronger in the downstream region and the position is south,the wave-current interaction leads to the enhancement of the upper jet over the south of China,and the high-altitude jet over the south of China is strengthened by the wave-current interaction.In southeastern China,there is strong water vapor convergence area,the ridge line of subtropical high is on the south side,the convergence configuration of high and low level divergence is strengthened,and the vertical ascending movement is enhanced,which is easy to cause the precipitation anomaly in the southern part of China.When the wave interaction flux divergence index WFD-I is a negative anomaly year,the ASWJ position is north,the wave interaction flux vector at the wave source is mostly northward,and the longitudinal propagation of Rossby wave energy is strong but the zonal propagation is weak,the key area of precipitation in northern China is controlled by the divergence of wave flux,the jet flow over the northern part of China is strong,the northern part of China is negative anomaly of water vapor fluxdivergence,and the upper level divergence and low level convergence are observed in the northern part of China.The convergence configuration of high and low level divergence and the vertical upward motion are beneficial to the development of precipitation in the northern part of China in summer.(5)Studying the circulation cause of precipitation anomaly in China caused by the wave activity flux divergence index WFC-II anomalous years over the eastern Qinghai-Xizang Plateau to the Loess Plateau in summer.It is found that the wave action flux divergence index(WFC-II)is in a normal anomalous year,the energy of Rossby wave in the upper reaches of South China is weak,the position of ASWJ is north,the propagation of Rossby wave is mainly in meridional direction,and the flux divergence of wave action in southern China is weak,the wave-current interaction is weak,and the water vapor flux divergence is strong in the south of China,the convergence ascending motion is weak,vertical circulation is not conducive to the development of precipitation in southern China.when the wave interaction flux divergence index(WFC-II)is a negative anomaly year,the convergence at the critical region II of the wave interaction flux convergence is strong,the wave-current interaction is weak,the jet flow position is south as a whole,and the water vapor flux divergence region is strong in the north of China.The position of the west Pacific subtropical ridge line is south,and the high and low spatial circulation configuration of the low level divergence and high level convergence makes the northern part of China become the whole subsidence movement,which is easy to cause the abnormal precipitation in the northern part of China.(6)In the Meiyu season of abnormal typical(atypical)Meiyu years,the wave flux in the eastern part of China is strong divergence(convergence),the wave-current interaction is strong(weak),the ASWJ intensity is strong(weak),the position of jet flow is south(unstable).In the Jianghuai area of China,the water vapor flux divergence is negative(positive)anomaly region,corresponding to the abundance(less)of precipitation in the abnormal typical(atypical)Meiyu years,the vertical circulation is strong(weak)and deep(shallow)vertical upward movement in the middle and low latitudes,which is not conducive to the development of deep convection,the whole layer E-P flux divergence is basically positive(zero)value,that is,the E-P flux divergence is relatively strong(no divergence),and the transient disturbance feedback makes the subtropical westerly jet intensity strong(weak).