白鹤滩水电站坝区极端大风天气分析

Analysis of a Catastrophic Gale Weather in the Dam Area of Baihetan Hydropower Station

利用常规观测资料和美国NCEP/NCAR再分析资料,从环流背景、物理量诊断、对流系统演变以及卫星和雷达遥感探测方面,综合分析2016年6月4日出现的有记录以来最强的雷暴大风天气的形成机制。结果表明:对流层中高层强烈干冷空气入侵与低层暖湿气流叠加,形成强烈的位势不稳定大气层结,为大风过程提供热力条件;对流层中高层的西风急流促进了高层的辐散运动,为过程提供动力条件;对流层低层的干冷空气堆促进水汽蒸发,使环境温度降低,加速冷空气下沉;在高空槽、中层切变线等天气尺度系统引导下,小尺度雷暴单体不断新生、合并,使得对流天气维持和加强;白鹤滩水电站坝区地形的“狭管峡谷效应”有利于风速的增大。

Based on the conventional observation data and NCEP/NCAR reanalysis data,the formation mechanism of the strongest thunderstorm gale weather on June 4,2016 was comprehensively analyzed from the aspects of circulation background,physical quantity diagnosis,convection system evolution and satellite and radar remote sensing detection.The results show that the strong invasion of dry and cold air in the middle and upper troposphere and the superposition of warm and wet airflow in the lower troposphere form a strong potential unstable atmospheric stratification,which provides thermal conditions for the strong wind process.The westerly jet in the middle and upper troposphere promotes the divergence movement in the upper troposphere and provides dynamic conditions for the process.The dry and cold air pile in the lower troposphere promotes the evaporation of water vapor,reduces the ambient temperature and accelerates the sinking of cold air.Under the guidance of synoptic scale systems such as high trough and middle shear line,small-scale thunderstorm cells continue to regenerate and merge,which makes convective weather maintain and strengthen.The"narrow tube canyon effect"in the dam area of Baihetan Hydropower Station is conducive to the increase of wind speed.