This paper has carried out the statistical and diagnostic analyses of development of cyclones in east sea area of China in spring from 2008 to 2014.Results show that the cyclones in east sea area of China in spring are shallow low-pressure systems.The vertical stretching height of the cyclones is below 600 hPa and the horizontal scale is less than 1 500 km.The strong weather with strong winds,big waves and heavy precipitation is mainly located in the southeast of the cyclone.The high wind jet region of cyclonic circulation of each level,which forms in the southeast of the cyclone,is called the cyclone jet.From the top to the lower,the jet axis of cyclone rotates counterclockwise in the vertical direction,which forms a funnel shape of cyclone with big top and small bottom.Cyclonic shear on the left side of cyclone jet is conducive to the maintenance of intensity of cyclone center,and the cyclonic shear on the left side of upper cyclone jets is correspond to the velocity convergence zone in the front of lower cyclone jets,which is beneficial for the cyclonic dynamic pumping and the strong vertical ascending motion in the southeast of the cyclone.The cyclone jets at different levels are configured to support the asymmetric structure of the cyclone and lead to the asymmetric distribution of cyclonic elements.Cyclone jet transports vertical helicity,horizontal helicity and sufficient water vapor into the cyclone and they are strongly lifted in the southeast of the cyclone,which enhances the release of condensation latent heat and prompts the development of cyclone and the strong weather area occurred in the southeast of the cyclone from thermal and dynamic aspects.The sea surface frontal temperature distribution in spring is beneficial to the enhancement of the cyclone jet,which reinforces the baroclinicity of the cyclone through non-adiabatic cooling in the northwest and non-adiabatic heating in the southeast of the cyclone.Environmenal westerly jet stream at high altitude is located in the right side of the cyclone,forming the whole deviation wind convergence,which effectively enhances the low level cyclone jet.Meanwhile,the momentum transports downward from the upper level and locates in the west side of the cyclone,leading to the development of weak current(i.e.the sinking branch of spiral structure of the cyclone) in the northwest of the cyclone,and then enhancing the spiral circulation of the whole cyclone,which makes the cyclone jet also begin to strengthen from the lower level.%对2008-2014年中国东部海域春季海上发展气旋进行了统计与诊断分析.结果表明:1)这类气旋属于较浅薄的低值系统,垂直伸展高度多在600 hPa以下,水平尺度多在1500 km以内.伴随的强天气为大风、大浪与强降水,落区主要位于气旋东南部.2)气旋环流各层的大风急流区构成了气旋的东南部位,称为气旋急流.从高层到低层,气旋急流轴在垂直方向上呈逆时针旋转,形成气旋上大下小的漏斗形状.3)气旋急流左侧的气旋式切变有利于气旋中心强度的维持,上层气旋急流左侧对应下层气旋急流前部流速辐合区,有利于气旋式动力抽吸及在气旋东南部形成强的垂直上升运动区.各层气旋急流配置导致气旋的非对称结构,以及气旋要素的非对称分布.气旋急流向气旋中输入螺旋度以及充足的水汽,并在东南部强烈抬升,增强了凝结潜热释放,从热力和动力两方面促进气旋发展及强天气落区.4)春季下垫面温度分布(锋区)有利于气旋急流的增强,并通过西北部非绝热冷却和东南部非绝热加热,增强气旋斜压性.高空环境西风急流位于气旋右侧,形成了整层偏差风辐合,有效增强低层气旋急流.同时高空动量下传位于气旋西侧,首先增强气旋西北部的弱流部分(即气旋螺旋结构的下沉支),进而增强整个气旋的螺旋环流,促使气旋急流也从下层开始增强.
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