1991年江淮梅雨期一个阻塞个例的Lagrange诊断分析

利用等熵面轨迹法,对1991年江淮梅雨期7月1日至7日的阻塞过程持续异常进行了诊断分析.等熵面位涡的分析表明,阻塞的维持与演变与等熵面上其高低压中心所对应的负正位涡中心的变化相一致.等熵面上等位涡线的轨迹积分表明,阻塞的形成、维持及衰减,对应着物质线裹卷的形成、维持(或加深)及不可逆形变和高低位涡的输送及积累的变化.同时发现,阻塞附近位涡系统的移动、演变和阻塞上游分流区位涡系统形变引起的瞬变涡度源的强迫作用,对阻塞的形成也有一定的作用.

A Lagrangian Diagnosis on a Block Case during the 1991 Meiyu Period in the Changjiang-Huaihe Region

A modified Lagrangian method on the iso-entropy surface to diagnose the persistency ab- normality of the block case during the 1991 Meiyu Period in the Changjiang-Huaihe region. The ana- lyses of IPV (potential vorticity field on the iso-entropy surface) show that the maintenance and variation of the block are corresponding to the variation of the systems on the IPV. Through integrating the iso-PV lines (material lines) on the iso-entropy surface, it shows that the building, maintenance and the disappearing of the block are corresponding to the building, maintenance (or extending) and the irreversible variation of the rolling up of the material lines. It was also found that the moving of the PV systems near the block and the forcing effect of transient PV origin, created by the deforming of the PV systems near the difflluent region in the upstream, are favorable to the building of the block.