贵州威宁对流单体雷达回波分层结构特征分析

Analysis of Radar Echoes Layered Structure Characteristics of Convective Cells in Weining,Guizhou

本文选取了2017—2020年威宁县111个对流单体(35个冰雹云单体和76个雷雨云单体),着重分析了对流单体雷达回波在垂直指向上的分层结构特征,并结合双偏振雷达观测分析了对流云单体偏振参量和水凝物相态分布特征。研究分析结果表明:①威宁对流单体雷达回波典型特征量基本一致,对流单体生命史周期约为100 min,最大反射率因子主要位于与0℃层高度差±2.0 km的范围内;②当对流单体雷达回波强度从45 dBz发展到55 dBz以上时,冰雹云具有发展迅速且持续时间长的特点,冰雹大小则与强回波在融化层高度以上的扩展高度存在一定的对应关系,高度越高、冰雹越大;③X波段双偏振天气雷达能够较好地反映降水粒子类型,基本符合粒子形状、大小和相态分布的特点,但应考虑降水相态粒子处于临界过渡区域的转化特点;④威宁多小冰雹主要与垂直风切变较弱、对流有效位能CAPE值不稳定能量偏低,且中小冰雹在下落过程中逐渐融化变小有关。

In this paper,111 convective cells(35 hailstorm cells and 76 thunderstorm cells)in Weining are selected to analyse the radar echoes’layered structure of convective cells in the vertical direction.The polarization parameters of the convective cloud and the phase distribution characteristics are analysed combined with the observation of dual-polarisation weather radar,preliminarily revealing that hailstorm cells have the characteristics of rapid development and small diameter of hail.The results are as follows:(1)The typical radar echo characteristic quantities of convective cells in Weining are basically consistent;the differences in macroscopic characteristic quantities are small,with the life cycle being about 100 min,and the maximum reflectivity factor mainly located within the height difference±2.0 km from the 0℃ layer.Hailstorm cells are stronger than thunderstorm cells and exhibit rapid development,longer duration,and greater stability.(2)The ratio of the mean value of the maximum reflectivity factor of hail cloud echo greater than that of the 0℃ layer is only 28.6%;the hail diameter≥10 mm accounts for only 8.3%,and the time for convective cells to develop into hail cloud cells is only 30 min,which is generally unfavourable for the formation of large hail.The size of hail corresponds to the spreading height of strong echo above the melting layer.The size of hail varies with the change of 45 dBz and 55 dBz echo development altitude;the higher the altitude,the larger the hail.(3)In general,there is little difference between hailstorm and thunderstorm,making it difficult to completely distinguish hailstorms.The X-band dual polarisation weather radar can reflect the type of precipitation particles and basically accords with the characteristics of the shape,size,and phase distribution of precipitation particles.It is necessary to introduce dual-polarisation radar observations,which is of great significance to improve the accuracy and lead time of hail recognition.However,the transformation characteristics of precipitation phase particles in the critical transition region should be considered,especially the interaction of Z hh,Z dr,K DP,ρHV,and other polarisations in the phase transition of particles.(4)The atmosphere in Weining is unstable,and the low-level humidity conducive to convective weather formation reaches more than 83%.However,the vertical wind shear is weak,and the unstable energy is low;only 20%of cases have unstable stratification and possess strong unstable energy.In addition,the melting effect in the falling process of medium and small hail makes it easier to produce small hailstones in Weining.