江淮流域持续性暴雨过程前期的欧亚波列特征及其模拟研究

利用50余年的NCAR/NCEP再分析资料,对江淮流域持续性暴雨过程前期的环流特征进行了相关与合成分析。发现在过程前2—1周的对流层中高层西风带上,中西亚、中国东部沿海和白令海南侧相继有低压槽发展,呈现显著的罗斯贝波列信号特征。分析表明,正是该欧亚波列的东传和消失伴随的环流调整,导致了有利于持续性暴雨产生的稳定环流的形成。进一步采用区域数值模式检验了该波列特征对后期持续性暴雨的作用和影响过程,以1991年一次典型的江淮流域持续性暴雨过程为例,根据欧亚波列信号特征设计一组初始流场扰动,进行初值集合模拟试验。结果表明,过程强雨带及其环流背景的模拟对于初始场上欧亚波列信号区的扰动特征是相当敏感的,该初始扰动对模拟环流的后继影响,与持续性暴雨期间稳定环流特征的建立和维持确有密切关系。

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.