1998年长江流域致洪暴雨的天气特点分析

Analysis of Rainstorm-Triggering Circulation Patterns in the Yangtze River Valley in Summer 1998

通过 1 998年夏季 (6— 8月 )天气图及部分资料的分析 ,对引起 1 998年夏季长江流域特大洪水的大到暴雨作了初步分析。结果表明 :1 998年夏季长江流域致洪暴雨的发生、发展是在一定环流形势下中低层中尺度系统活动频繁而造成的。还提出了 1 998年夏洪峰降水的两种环流模型 ,即副高西进低槽东移型和副高稳定且切变线上有西南涡活动型。并指出 :当这两类暴雨环流型出现越频繁 ,暴雨出现次数越多时 ,长江流域易涝 ;反之 。

A rainstorm that caused a severe flood along the Yangtze River Valley in summer 1998 is investigated on the basis of weather maps and other data.The result shows that the occurrence and development of the flood-causing rainstorm is triggered by frequent activitives of mesoscale systems in the middle- and low- atmosphere under certain circulation pattern.Two circulation patterns which cause the rainstorm and lead to the flood peak in the valley are put forward,namely:pattern of strengthening subtropical high and eastward-moving trough;pattern of stable subtropical high and frequent southwest eddy activitives on shear line.It is concluded that the more(less) frequent of the appearance of the two patterns and rainstorm, the more likely the formation of flood(draught) in the valley.