The Summer Northeast China Cold Vortex's Initial Position Variation And Its' Impact On Meiyu Over The Yangtze-Huaihe River

Based on the ERA-Interim reanalysis data provided by European Centre for MediumRange Weather Forecasts(ECMWF)and the precipitation data in the "Daily data set of basic meteorological elements of China's national surface meteorological stations(V3.0)",with reference to the climate zone and the begin-end date according to the monitoring index of Meiyu,this paper discusses the variation characteristic of the Northeast China cold vortex(NECV)'s initial position in summer from 1979 to 2018 and its influence on Meiyu of each district.The conditions of atmospheric circulation are analyzed.The result shows that:(1)The frequency of NECV formation is the most in the northwest and the least in the southeast in summer.As far as June is concerned,the initial position of the NECV is located further north in the 1980 s while the plum rain is more in the north and less in the south,further south in the 1990 s while the plum rain is less in the north and more in the south.The initial position has a periodic oscillation for about 3 years,which is consistent with the meiyu intensity in Jiangnan region,Jianghuai region and the regional average precipitation in Jiangnan region.(2)In the plum rain season,the strong southward airflow behind NECV can guide the cold air to the south,and the change of the initial position of NECV affects the location of cold air and the intersection of the cold and warm air,thus affecting the spatial distribution of the plum rainfall.The year in which the initial position of NECV is located further northwest,the airflow at low level in the Jianghuai region is prone to cyclonic convergence,advantageous to the vertical upward movement.Moreover,the strong water vapor transport in the southeast of the shear line of water vapor transport brings abundant water vapor resources to this region,which increases the rainfall of plum.However,the year in which the initial position of NECV is located further southeast,the shear line of low-level water vapor transport moves southward to the Yangtze River and the cyclonic convergence center of the lower air flow moves southward to the Jiangnan region,making the vertical upward area move southward,too.And the water vapor transport shear line moves southward,along the Yangtze river,the water vapor convergence provides necessary condition of water vapor for rainfall increasing in Jiangnan region and then the increasing rainfall area of Meiyu moves southward from the Jianghuai area to the Jiangnan area.