Abstract:The midlatitude cyclone is a low-pressure vortex with strong baroclinicity that occurs in the mid-to high latitudes in the Southern and Northern Hemispheres.Some studies show that significant changes in the cyclone activity and atmospheric circulation over East Asia have occurred over the past decades.The statistical characteristics of the midlatitude cyclone were analyzed manually in the past,while this method is time-consuming and relies on the subjective experience of researcher.The objective cyclone identification and tracking method is widely used to research on detecting cyclone activities with the development of reanalysis data and numerical model in recent years.The features of precipitation in Northeast China in spring and summer and its relationships with mid-to high latitude circulation systems are well studied.The cold vortex in Northeast China is considered as the key component,while midlatitude cyclone also plays an important role in rainy season.In this study,based on the 4 times daily ERA-Interim mean sea level pressure reanalysis data,using the objective cyclone identification and tracking method,the characteristics of mid-latitude extra-tropical cyclone activity in East Asia in spring and summer during 1979-2013 and its linkage with concurrent rainfall in Northeast China are analyzed.The results show that East Asian mid-latitude cyclones generate in the middle of Mongolia and to the east of Altai Mountains,and move to the north of Heilongjiang province.The cyclone increases gradually to the maximum to the west of Greater Khingan Mountains and dissipates thereafter.The region of cyclone activity in spring is larger than that in summer,and the cyclone is also stronger in spring.While the lifetimes of cyclone are similar in different seasons,the maximum standard deviation of cyclone frequency and intensity are both located in central Mongolia,which indicates that both the most frequent cyclone activity and the greatest variation of cyclone activity happen there.Therefore,Mongolia was selected as the representative area for the abnormal activity of midlatitude cyclone in East Asia.The cyclone numbers in spring and summer in this key area (40-50°N,80-140°E) both display linear decreased trend in the late 35 a.The correlation between the cyclone activity and rainfall in Northeast China is positive in both seasons,but the reasons are different.During the strong cyclone activity years,the cyclonic circulation over Northeast China benefits the increase of spring rainfall,and the increase of summer rainfall mainly depends on the anomalous westerly moist transport.