山东较大范围致灾雷暴大风的多普勒天气雷达特征

Doppler Radar Characteristics of Wide-Range Damaging Thunderstorm Gales in Shandong Province

利用多源观测资料对2005—2021年山东和周边地区较大范围致灾雷暴大风事件及造成此类事件的对流系统的雷达回波特征从两个尺度进行了分析,结果发现:17年间共发生41次较大范围致灾雷暴大风事件,年均发生2.4次,主要发生在6月。发生前,对流层中下层具有明显的条件不稳定,湿度条件中等略偏干,中层具有明显干层,垂直风切变中等略偏强。就导致较大范围致灾雷暴大风的对流系统整体而言,可分为Ⅰ型(单体可分辨形)飑线、Ⅱ型(条形)飑线、多单体风暴群和弱回波型飑线四类。后侧入流急流携带干冷空气进入飑线通过蒸发冷却降温增强负浮力是Ⅰ型飑线和Ⅱ型飑线产生致灾雷暴大风重要机理。后(右)向传播的多单体风暴群均伴有超级单体,其阵风锋一方面能够触发新生风暴,另一方面本身也可以产生致灾雷暴大风。强对流风暴本身较快的移动速度和可能的后侧入流急流在系统内由降水触发的下沉气流作用下产生的动量下传,导致非对称的下击暴流,增加了出现极端雷暴大风的可能性。弱回波型飑线产生的致灾大风最易被忽视。直接造成120站次致灾雷暴大风的对流分系统包括弓形回波、非超级单体强单体、超级单体、阵风锋和混合型五类,占比分别为30%、26%、6%、23%和16%。弓形回波和超级单体产生的致灾雷暴大风极大风速平均值最大,分别为28.2 m·s^(-1)和29.9 m·s^(-1)。强后侧入流急流和显著中层径向辐合特征可提前约20 min预报弓形回波的形成。致灾雷暴大风主要出现在弓形回波移动方向的中间部分和左侧部分。阵风12级及以上的极端雷暴大风由镶嵌弓形回波的波动型线状回波、弓形回波与中尺度涡旋的组合以及超级单体产生。具有深厚中层径向辐合的非超级单体强单体、强烈发展的飑线的阵风锋、地面冷锋与阵风锋的叠加(常伴有高空动量下传)均可能产生30 m·s^(-1)左右的雷暴大风。

Based on multi-source observation data,the radar-echo characteristics of wide-range damaging thunderstorm gale events and the associated convective systems in Shandong Province and surrounding areas from 2005 to 2021 are analyzed.The results show that there were 41 wide-range damaging thunderstorm gale events in the 17 years,with an annual average frequency of 2.4 times,and they mainly occurred in June.Before the occurrence of damaging thunderstorm gale,there tends to be remarkable conditional instability and moderate-to-slight humidity condition in the middle and lower troposphere.Meanwhile,there is a prominent dry layer in the middle level,and the vertical wind shear is moderate-to-slightly strong.The convective systems that lead to wide-range damaging thunderstorm gales can be divided into four categories:typeⅠsquall line(cell resolvable type),typeⅡsquall line(banded-echo type),multicell storm cluster and weak echo squall line.The rear inflow jet carries dry-cold air into the squall line and enhances the negative buoyancy through evaporative cooling effect,which is an important formation mechanism of damaging thunderstorm gale generated by typeⅠand typeⅡsquall lines.The backward(or rightward)propagating multicell storm clusters all contain supercells,whose gust front can both produce damaging thunderstorm gale and trigger new storms.Due to the fast moving speed of the severe storm and the possibly-existing rear inflow jet,as well as the downward transport of momentum from high levels caused by the downdraft in the precipitation,the asymmetric downburst can occur,which increases the possibility of extreme thunderstorm gales.The damaging thunderstorm gales generated by the weak echo squall lines are most likely to be ignored.The convective subsystems that directly cause damaging gales can be classified into five categories,namely bow echo,strong single cell storm,supercell storm,gust front and mixed type,accounting for 30%,26%,6%,23%and 16%,respectively.The average values of the maximum wind speed caused by bow echo and supercell are the largest,reaching 28.2 m·s^(-1)and 29.9 m·s^(-1)respectively.The formation of bow echo can be predicted about 20 minutes in advance according to strong rear inflow jet and remarkable mid altitude radial convergence(MARC).The damaging thunderstorm gale mainly occurs in the central and left parts of the bow echo relative to its moving direction.Extreme thunderstorm gales with wind speed over 32.6 m·s^(-1)are generated by the line-echo wave pattern embedded with bow echoes,the combination of bow echo and mesoscale vortex,and supercells.Thunderstorm gales at the speed about 30 m·s^(-1)can be produced by the strong single cell storms with deep MARC,the gust fronts in strongly developed squall lines,and the superposition of surface cold front and gust front which is often accompanied by downward momentum transportation.