山东“7.18”致灾暴雨成因分析

Causal Analysis of a Diaster-Inducing Rainstorm in Shandong Province

利用实况观测资料、中尺度自动站资料和NCEP再分析资料,对2007年7月18日山东省大暴雨过程进行了诊断分析,同时还分析了暴雨致灾原因。结果表明,本次大暴雨是由高空冷涡南部的低槽、底层准东西向切变线、副热带高压西北边缘的暖湿气流以及来自东北南下冷空气共同影响所致。低层前期明显的持续升温为暴雨的产生创造了极好的热力条件,强盛的低空西南暖湿气流输送为此次暴雨提供了充足的水汽,同时山东上空低层高温高湿、能量增大,形成上干冷下暖湿的对流性不稳定层结。沿850 hPa切变线北侧东北气流迂回南下的冷空气与低空西南急流携带的暖湿空气在山东交汇,冷暖空气在对流层低层相互作用,具有明显的暖锋锋生特征,弱冷空气的低层侵入对暖湿空气具有抬升作用,促使对流发展和不稳定能量释放产生暴雨。地面存在中尺度辐合中心或辐合线的生成和发展,是这次大暴雨产生的启动机制,大暴雨的分布与地面辐合线的走向基本一致。降水历时短强度大,特殊的地势地貌是本次暴雨致灾的重要原因。

With observational data,mesoscale automatic weather station data and NCEP reanalysis data,a diagnostic analysis is made of the causes of a severe heavy rain occurred on 18 July 2007 in Shandong Province.The results show that the rainstorm was caused by the interaction of the westly trough originated from the cold vortex over the northeast China,the quasi east-west oriented shear line at lower levels,and the warm and wet airflow on the northwest edge of the subtropical high and cold air from northeast.It is found that the continued warming and strong warm-wet air transport at lower levels provided excellent thermal conditions and adequate water supply.Meanwhile,the convective unstable stratification was formed over Shandong Province.Along the shear line at 850 hPa,the northeast wind with cold air and the low-level southwest jet with warm air converged.Because of the interaction between the two airflows in the low troposphere,the warm front had obvious characteristics of frontogenesis.The uplifting of warm air caused by the weak low-level cold air intrusion promoted the development of convection and energy release.The mesoscale convergence center or convergence line activated the mechanisms of rainstorm formation,and the distribution of heavy rainfall had the same direction with the ground convergence line.The strong rainfall intensity and the special terrain topography played an important role in this rainstorm-induced disaster.