一次典型飑线过程多普勒天气雷达资料分析

Analysis on a Typical Squall Line Case with Doppler Weather Radar Data

对2002年8月24日发生在安徽的一次大范围飑线过程进行了分析。该飑线影响范围大、持续时间长,产生于对流层中高层槽后干冷空气向南大范围扩散,低层辐合,大气层结非常不稳定,深层大气垂直风切变中等的背景下,在其影响的广大区域产生大风和部分地区的冰雹和暴雨。雷达回波呈现弓形,伴有明显的雷暴出流边界(阵风锋),与弓形回波相对应的多普勒径向速度明显地预示地面大风的中层径向辐合(MARC)。而中气旋的存在,通过加速干冷空气向雷暴内的夹卷,加强了下沉气流。另外,弓形回波前沿中低层存在弱回波区,中高层存在回波悬垂,强回波区延伸到-20℃等温线之上,表明雷暴内上升气流很强,有利于大冰雹和强降水形成。分析还表明雷暴出流边界与雷暴之间距离的变化在一定程度上可以预示未来雷暴强弱的变化。

A typical case of squall line occurred in Anhui Province on 24th August 2002 is analyzed,using the Hefei Doppler weather radar data,routine upper-air and surface data,and intense surface observation data.The synoptic background is featured by the southward invasion of mid-level troposphere dry and cold air behind the westward moving trough,lower level convergence,extreme unstable air and moderate vertical wind shear.The squall line produced high wind in a very large area,hail and heavy rain in some areas.The radar echo displays ／!bow／＂ shape,with a clear outflow boundary（gust front） in front of it.Corresponding to the bow echo in reflectivity image,the velocity image shows significant mid-level radial convergence（MARC）,indicating strong wind in surface afterwards.Furthermore,above the leading edge of the bow echo,there is a weak echo region and a echo overhang above it,and the strong echo extend up above the-20℃ level,implying strong updraft in the storms,favorable for the severe hail and heavy precipitation.The analysis also shows that the variation of the distance between the gust front and thunderstorm can,to some degree,indicate the future trend of the thunderstorm.