2016年山东一次阵风锋触发的强对流天气分析

Analysis of the severe convective weather caused by a gust front in Shandong in 2016

利用常规观测、区域自动气象站、NCEP/NCAR再分析和雷达回波资料,对2016年6月30日山东一次阵风锋触发的强对流天气进行了分析。结果表明,此次强对流主要发生在高空槽与副热带高压相互作用、山东高低层受一致西南气流影响的环流形势下,阵风锋、地面辐合线和负变压中心所产生的抬升作用及近地面层冷空气的侵入使气温骤降是触发对流的关键因素。低层水汽充沛、湿层厚,属于上干下湿的不稳定层结。强对流发生区域处在假相当位温差(Δθse)和风暴相对螺旋度(storm relative helicity,SRH)的大值中心及其右侧位置。对流有效位能(convective available potential energy,CAPE)、850 h Pa与500 h Pa之间温差、大风指数、强天气威胁指数等都对此次强对流有较好的指示作用。0℃层高度和融化层高度较高是此次过程未出现大冰雹的原因。较强的0~3 km垂直风切变在强对流预报业务中需要注意。此次强对流过程是线状回波带前侧风暴内出现了阵风锋,阵风锋又不断触发雷暴使个别强单体风暴发展加强成为超级单体风暴,具有持续时间较短的中气旋、高悬的强回波、有界弱回波区、风暴顶辐散、窄带回波、径向速度大值区等回波特征。风暴移动速度比风暴承载层平均风速大,缩短了超级单体存在时间。此外,风暴参数与天气的强烈程度密切相关。

Based on the data from conventional observation, regional automatic weather stations,NCEP/NCAR reanalysis and radar echoes,the severe convective weather caused by a gust front in Shandong on 30 June 2016 is analyzed. The results indicate that the convection happens when the upper trough and subtropical high interact with each other and Shandong high and low layer are affected by southwestern air flow. The uplift effect from the gust front,ground convergence line and katallobaric center and the sudden temperature drop from the invasion of the ground layer cold air are key factors in triggering the convection. The process occurs under an unstable stratification where it is dry and cold at the upper level,wet and warm at the lower troposphere. The water vapour at the lower layer is abundantand wet layer is thick. It occurs in the center and right side of the high value region of θse 850-θse 500 and SRH. CAPE,temperature difference between 850 h Pa and 500 h Pa,WINDEX,and SWEAT index are indicative to the convective weather. The cause of no big hail is that the height of 0 ℃ layer and melting layer is higher. The stronger vertical wind shear from 0 to 3 km needs attention in the convection forecast.During the convection,in the front storm of the linear echo band there appears the gust front,which constantly triggers thunderstorm and several strong single-cell storms develop into supercell storm. Echo characters are the mesocyclones that have short duration,raised strong echoes,bounded weak echo zone,the divergence at the top of the storm,narrow-band echoes,high value zone of radial velocity,etc. The moving speed of the storm is larger than the average wind speed of its bearing layer,which reduces the existence time of the supercell. In addition,storm parameters are related to the intensity of weather.