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

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.