一次引发暴雨的东北低涡的涡度和水汽收支分析

对2005年7月25～29日引发较大范围持续性暴雨的东北低涡的结构、涡度和水汽收支进行了分析研究,结果表明:1)东北低涡是一个较深厚的冷性涡旋.初期,气旋性涡度出现在对流层中层,然后向中低层及高层伸展.而低涡加强阶段,气旋性涡度在对流层高层增加得最快,并逐渐向中低层传播,诱发地面气旋的发展;由于高低空锋生的相互作用,在低涡南部形成了深厚的近乎垂直的低层略前倾的"弓形"锋区.2)对涡度收支的计算表明,水平涡度平流项和水平辐散项对低涡的发展、加强起到最主要的作用.但在不同阶段,这两项的作用和大小各不相同.3) 对流层高层位涡大值区在低涡东部向下传播,有利于低涡的发展加强,与低涡暴雨的落区位置较为接近.此外对卫星云顶亮度温度(TBB)的分析,发现低涡暴雨典型的涡旋云带中对流活动旺盛的地区与局地暴雨的位置对应.4) 低涡暴雨的水汽初期主要来自北部,随着低纬地区西南季风的增强,沿副高西侧从低纬到中高纬建立起一条较强的水汽输送带,东北地区水汽收支以南北向的辐合为主.5)将2005年和1998年夏季6～8月的东北低涡暴雨个例的天气形势配置进行逐月比较,发现持续的较大范围的低涡暴雨过程与亚洲中高纬的阻塞形势、低涡的维持、西太平洋副热带高压的位置及夏季风和低纬系统的水汽输送有密切的关系.

Study of the Vorticity and Moisture Budget of a Northeast Vortex Producing Heavy Rainfall

Detailed analysis are conducted on the structure,the vorticity and moisture budgets of a northeast vortex which caused sustained heavy rainfall in Northeast China on 25-29 July 2005.The results show: 1) The northeast vortex was a deeper depression related with cold air.In the early formation stage,the cyclonic vorticity appeared in the middle troposphere and then extended to the lower and upper level,respectively;While in the developing stage of the vortex,the cyclonic vorticity increased most rapidly in the upper troposphere,then extended downwards to the middle and the lower troposphere,which produced the development of surface cyclone with front.Under the interaction of frontogenesis between upper and lower level,there formed a nearly vertical deep "Bow-Shaped" front zone with a little tilted forwards in the low level.2) The calculation of vorticity budget indicates that both the horizontal advection term and horizontal divergence term contributed most significantly to the strengthening of vortex,but their values are different during the different stages of the vortex.3) The maxima of the potential vorticity anomaly were located in the upper troposphere,and then extended downwards in the southeastern part of the vortex which is near the area of heavy rainfall.In addition,the analysis of satellite data TBB shows that there existed the typical spiral cloud band during the period of the heavy rainfall and the area of intense convective activities coincided with that of heavy precipitation.4) In the early stage of heavy rainfall of the northeast vortex,the moisture budget was mainly from the north boundary;With the reinforcement of southwest monsoon in the low latitude,a moisture transportation from the low to the middle or higher latitude was formed along the west edge of subtropical high and the moisture supply is mainly caused by the convergence of north and south boundary.5) Finally,comparison has been conducted between the heavy rainfall cases of northeast vortexes during the summer of 2005 and 1998,and it shows that the sunstained heavy rainfall in larger area was closely related to the Asian blocking highs in middle or higher latitude,the maintenance of vortex and the position of subtropical high in West Pacific,as well as the moisture supply of summer monsoon coming from low latitude area.