The Influence Of The East Asian Westerly Jet Rossby Wave Energy Propagation On The Rainfall Anomalies In The Yangtze River Basin During The Rich And Dry Plum Years

Based on the waveguide structure along the westerly jet,the wave-activity fluxes,wave energy equation and the wave packet to diagnostic methods,this paper systematically studies the propagation and evolution characteristics of Rossby wave energy along east Asian westerly jet during the precipitation anomalies of the Yangtze river basin before Meiyu,during Meiyu and after Meiyu in heavy and light Meiyu years.Moreover,the conceptual model of wave energy propagation characteristics is preliminarily established.The analysis results show that:1? The Rossby wave is active in a wide range of waveguide regions in heavy Meiyu years.Before Meiyu,the waveguide regions in the east of the Arabian peninsula and in the south of the middle reaches of the Yangtze river basin are stronger in heavy Meiyu years than in light Meiyu years.Combined with the distribution of wave barriers,the propagation of Rossby wave and the dispersal to the downstream of energy are more favorable in heavy Meiyu years.During Meiyu,the intensity of waveguide region in the eastern part of the Arabian peninsula decreases greatly both in heavy and light Meiyu years.The Rossby wave,which develops from the east of Arabian peninsula to the northeast before Meiyu in heavy Meiyu years,forms two waveguide regions in the middle and upper reaches of the Yangtze river basin during Meiyu,while there is only a small one in light Meiyu years.After Meiyu,in the upper reaches of the Yangtze river basin,the waveguide regions weaken and disappear in heavy Meiyu years which are strong in light Meiyu years.2? The large value regions of the wave-activity fluxes are basically located from north African to west Asia region and the north of the middle and lower reaches of the Yangtze river basin in heavy and light Meiyu years,and the strong positive disturbance center in Asia moves westward continuously.The variations of the wave-activity fluxes in the north of the middle and lower reaches of the Yangtze river basin are as follows: it strengthens during Meiyu and weakens after Meiyu in heavy Meiyu years,while weakens continuously in light Meiyu years.Before Meiyu,the wave-activity fluxes in the north of the middle and lower reaches of the Yangtze river basin is weak in heavy Meiyu years and strong in light Meiyu years.During the time,the disturbed stream function basically in a distribution state of negative-positive-negative.Before Meiyu,a strong positive disturbance center located in the middle and upper reaches of the Yangtze river basin is beneficial to the development of disturbance in heavy Meiyu years.However,the disturbance value of the Yangtze river basin in light Meiyu years is about 3*106m2/s smaller than that in heavy Meiyu years and the development of disturbance is relatively weak.During Meiyu,the wave-activity fluxes in the north of the middle and lower reaches of the Yangtze river basin strengthen in heavy Meiyu years.After Meiyu,it weakens obviously both in light and heavy Meiyu years.And the wave-activity fluxes are slightly larger in heavy Meiyu years in the north of the middle and lower reaches of the Yangtze river basin.3? There is mainly a conversion between the kinetic energy of the basic flow and that of the disturbance along the east Asian westerly jet stream.Above the north of the Yangtze river basin is mainly distributed as "the wave sink region-the wave source region-the transition region" in heavy Meiyu years,and distributed as "the wave sink region-the wave source region-the wave source region " in light Meiyu years.There is a wave sink region in the middle of central Asia before Meiyu in heavy Meiyu years,which corresponds to a conversion from the turbulent kinetic energy to the kinetic energy of the basic flow.By this way,the intensity of east Asian westerly jet increases and it provides a good transport channel for the propagation of Rossby wave.The absence of this wave sink region before Meiyu in light Meiyu years is an important reason that the propagation of Rossby wave is less vigorous than that in heavy Meiyu years.4? The large value regions of wave packets in the Eastern Hemisphere are mainly zonally distributed,and the distribution of the 3-8d high-frequency disturbance wave packets and the 10-15 d ultra-long wave packets with stronger amplitude are the same.In heavy Meiyu years,the large value center of the wave packets in the middle and low latitudes with a small distribution range is weak which is strong in the middle and high latitudes with a wide distribution range.Before Meiyu and during Meiyu,large value regions of wave packets are distributed around the Yangtze river basin in heavy Meiyu years.In combination with the wave disturbance and the distribution of waveguide in the entrance of jet stream,an effective channel for wave packets to transport wave energy is provided.In light Meiyu years,the distribution of large value regions of wave packets at middle and low latitudes shows that the large value centers of wave packets at the south of the Mediterranean Sea before Meiyu,the north of the middle and upper reaches of the Yangtze river during Meiyu and the middle and low latitudes after Meiyu are all stronger and wider than those in heavy Meiyu years.And the large value regions of wave packets in the Yangtze river basin are unfavorable for the propagation of wave energy to the downstream under the condition of weak waveguide.The meridional movement of wave packets in the middle and low latitude regions in light Meiyu years are stronger than that in heavy Meiyu years,which is not conducive to the propagation of wave energy.