广东罕见特大致洪暴雨形成机理个例分析

利用常规观测、雷达卫星和NCEP 1°×1°格点资料,从形势场配置、水汽供应、动力机制等方面对广东罕见特大暴雨的形成机理进行诊断分析。结果表明:西太平洋副高位置偏南,强度偏弱,副高北侧的西南暖湿气流与西风槽前的冷空气共同作用是此次特大致洪暴雨形成的重要原因;强盛低空急流为暴雨过程提供了充沛的水汽;高层辐散低层辐合激发强烈上升运动;特大暴雨过程中垂直螺旋度量级(10-6hPa.s-2)比常规(10-8hPa.s-2)大2个量级,其正值区长轴与700 hPa的切变辐合线走向和移动方向一致;广东暴雨范围和量级增大期间,其上空垂直螺旋度具有中低层正、高层负螺旋度闭合中心向低层明显传送的特征。

Formation Mechanism Analysis of a Flood Inducing Heavy Rain in Guangdong Province

The mechanism analysis of a flood-inducing heavy rainfall occurred in June 2005 Guangdong Province is diagnosed by analyzing the circulation situation,moisture,dynamical mechanism,vertical helicity,and so on based on the conventional observation data,radar echo,satellite image and NCEP grid data.The results show that the causes of the heavy rainfall include the farther south and weaker-than-normal ridge position of the West Pacific subtropical high and the interaction between the southwest warm and wet airflow to the north of the subtropical high and the cold air in front of the westerly trough;the low-level jet stream provides enough moisture;the divergence in high level and the convergence in low level resulted in strong updraft;the vertical helicity is two orders of magnitude greater than normal with the long axis of the positive vertical helicity area having the same direction with the movement of the shear convergence line on 700 hPa.During the heavy flooding rainfall,there was an enclosed negative center of vertical helicity at the middle level and an enclosed positive center at the upper level,spreading obviously down to the lower level.