Statistical and numerical study of the Rossby wave train signal over Eurasia prior to persistent heavy rainfall events over the Yangtze-Huaihe River valley

Based on the NCEP/NCAR reanalysis data from 1951 to 2004,the correlation and composite analyses are conducted to identify the characteristics of the circulation prior to the persisten the avyrainfall(PHR)events over the Yangtze and Huaihe river valley.The results show that on the middle and upper troposphere,a prominent Rossby wave train occured over Eurasia continent in two to one weeks before the events,three troughs respectively at central-western Asia,the eastern China coast and southern Bering Sea developed in succession.It is the significant modulation of large scale circulation accompanied with the dis-persion and disappearance of the Rossby wave train over Eurasia to finally result in the formation of stable circulation character-istics favoring the PHR events over the area under study.As the emphasis part of this paper,an experiment of ensemble numerical simulation was conducted for a typical PHR event in 1991 by using the regional numerical model MM5,to inspect the influence of that wave train signalon the subsequent PHR event.To carry out the ensemble simulation,a series of initial wind disturbances which are defined by the characteristics of the Rossby wave train signal over Eurasia,were imposed on the initial conditions of the control experiment.The results indicate that the simulation of the PHR event and the corresponding circulation characteristics are quite sensitive to the wave train signal over Eurasia.The subsequent influences of the initial disturbances with the characteristics of that signal were closely related to the establishment of the stable circulation features during the PHR event.