“2001.9.18”华西突发性强暴雨的中尺度分析

Mesoscale Analysis on "2001.9.18" Spate Heavy Rain in West China

利用地面、高空和卫星观测等资料,分析了2001年9月18～20日发生在青藏高原东侧的强暴雨天气过程,揭示了暴雨的激发机制和若干中尺度特征。主要结果是:(1)导致本次突发性强暴雨天气的中尺度系统是在一天内,在同一区域重复新生的2个中—β尺度对流云团。(2)边界层东南低空急流的不断加强和非地转变化对强降水天气起积极作用。(3)在强降水天气发生的每一时段,散度变化均较涡度变化对强降水天气的指示性好,前者与暴雨的关系更为密切。(4)大气运动非平衡强迫激发气流辐合增长是强降水天气的主要激发机制,未来12h强降水发生的区域、降水强度、中心变化与非平衡强负值区变化相一致。

By using the conventional and satellite data, the spate heavy rain event in west China during 18～20 September 2001 is analysed.The results are as fallows: (1) The heavy rain event was caused by two mesoβscale convective cloud clusters that occurred in the same region on 19 September 2003. (2) The steady enhancement of boundary lowlevel jet and its ageostrophic variance contribute to extreme heavy rain. (3) The relationship between divergence variance and precipitation in future 12 h is closer than vorticity variance. (4) The convergence increase which is enhanced by unbalanced dynamic force is the major dynamic trigger mechanism of mesoβscale heavy rain system as well as the occurring of the heavy rain.