一次四川暴雨过程的非线性对流-对称不稳定分析

The Analysis of Nonlinear Convective-Symmetric Instability in a Rainstorm in Sichuan

以NCEP/NCAR再分析资料和区域加密观测资料为背景场对2004年9月3—5日四川省一次特大致洪暴雨过程进行数值试验。在对降水模拟有较好结果的基础上,用模式大气资料分析了暴雨过程的非线性对流—对称不稳定,结果表明,近地面层条件性不稳定和地形强迫的共同作用触发了对流,而中高层的条件性对称不稳定促进对流的进一步发展,由此引发的深厚湿对流形成了持续大暴雨。

This paper carries out a numerical experiment on a flash-flood-producing rainstorm process from 3 to 5 September 2004 in Sichuan province, using NCEP/NCAR data and regional observational data as the background field. Because of the good precipitation simulation, the model outputs are used to analyze the non-linear convective symmetric instability of the storm. The results show that joint action of conditional instability and topographic forcing on the near-surface layer triggered the convection, then conditional symmetric instability at middle and high levels further promotes the convection. This process produced the vigorously developed deep moist convection and resulted in such a heavy and long-lasting rainstorm.