ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Propagation of Rossby Wave Along Asian Subtropical Westerly Jet in Summer and Its Impact on Anomaly of Precipitation in China
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Abstract:
By using the NCEP 2.5°×2.5° daily reanalysis data and daily precipitation data at 20:00 BT from Chinese meteorological stations in the summer of 1960-2015 (June-August), and the method of vorticity source equation and Eliassen-Palm flux, the wave sources, energy propagation of Rossby wave activities along the Asian subtropical westerly jet (ASWJ) in summer and its correlation with precipitation and anomalies in China are analyzed. The results show as follows. The sources of the quasi-stationary planetary waves at 200 hPa are mainly concentrated in the Mediterranean Sea, where the quasi-stationary Rossby waves in the Asian westerly jet are triggered and propagate eastward along the jet stream. In the process of eastward propagation, the wave-mean flow interactions in the southern side of the jet axis are relatively active. The convergence and divergence centers of the wave activity flux alternately distribute along the subtropical westerly jet, and the wave-mean flow interactions are the dynamic mechanism of the alternating variation of westerly intensity over ASWJ. The divergence of the five key areas of the wave action flux distributed alternately along ASWJ has a strong correlation, which is shown as different parts of the same Rossby wave train, of which the propagation of the Rossby wave energy at the wave source has the greatest influence on the strength of its downstream ASWJ.The magnitude of the zonal wind in the critical region of the jet stream is also closely related to the intensity and distribution of the divergence field of the wave-acting flux. The wave source flux divergence indices WFD-Ⅰ and WFC-Ⅱ which are located in the wave source and from the east of the Qinghai-Tibet Plateau to the Loess Plateau in China are more correlated with precipitation in southern and northern China. Statistical analysis in the summers of 56 years shows that when the WFD-Ⅰ is positive anomalous year, the proportion of precipitation in the key areas of the south is 62.5%, and when it is negative anomalous year, the proportion in the key areas of the north is 80%. When WFC-Ⅱ is positive anomalous year, the proportion in the key areas of the south is 66.7%, and when it is negative anomalous year, the proportion in the key areas in the north is 81.8%. Studying the circulation cause of precipitation anomaly in China caused by the wave activity flux〖HJ〗 divergence index WFD-Ⅰ anomalous years at wave source in summer, we find that when WFD-Ⅰ is positive anomalous year, the Rossby wave triggered by the upstream source region has a strong energy dispersion to the downstream region and the position is southerly, the wave-mean flow interaction leads to the intensification of high-altitude jet over southern China, the intensification of divergence and convergence configuration at high and low levels, and the intensification of vertical ascending movement, which are liable to cause more precipitation anomalies in southern China.When WFD-Ⅰis negative anomalous year, the meridional propagation of Rossby wave energy is stronger, while the zonal propagation is weaker. The key area of northern precipitation is controlled by wave activity flux divergence, the westerly jet at high altitude is strengthened, the divergence and convergence configuration at high and low levels and the vertical ascending motion are enhanced, which are beneficial to the development of precipitation in northern China.
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