一次南岭山脉前汛期强对流天气过程诊断分析

Diagnostic analysis of a severe convective weather event in the Nanling Mountains during the pre-rainy season

利用常规观测资料、FY-2G/2E卫星黑体亮温(TBB)资料、多普勒天气雷达资料与ERA-Interim再分析资料,对2016年4月17—18日南岭山脉一次强对流天气过程进行了诊断分析。结果表明:(1)该过程前期,受地面倒槽与辐合线影响出现暖区降水,后期随着地面冷空气侵入配合低空切变线与高空槽东移南压迅速转变为锋面降水,强降水落区与南岭山脉走向一致,大暴雨由多个中尺度对流系统(MCS)移入和有利地形作用造成;大冰雹、雷暴大风主要出现在暖区降水时段,暖区短时强降水以高质心降水为主,锋面越山之后强天气主要为低质心短时强降水,雷暴大风和冰雹较少出现。(2)雷达回波图上中层径向辐合的出现,对雷暴大风具有预警参考意义;中气旋、高垂直累积液态水含量(VIL)、回波悬垂、有界弱回波等回波特征对提前预警大冰雹有一定的指示作用。(3)不同类型强天气发生的大气层结条件存在差异,上层干区深厚、低层湿度条件较好有利于产生大冰雹,大的0—6 km垂直风切变有利于冰雹增长;大的下沉对流有效位能(DCAPE)是预报雷暴大风的一个参考指标;整层温度露点差和DCAPE小是判断只出现短时强降水的参考依据。(4)南岭及其附近地区"喇叭口"地形和迎风坡地形有利于低层气流辐合触发对流,造成暴雨多发和降水时间延长,南岭背风坡的锋生作用使南岭山脉南麓出现雷暴大风、冰雹等天气的可能性增大。

Based on the routine upper-air and surface observations,temperature of brightness blackbody(T BB)from FY-2G/2E satellite,Dop-pler weather radar data and reanalysis data from ERA-Interim,we have conducted the diagnostic analysis of a severe convective weather event occurred in the Nanling Mountains from April 17 to 18 in 2016.Results are as follows.(1)Affected by inverted trough and convergence line at ground level,warm area precipitation occurred in the preceding stage of this event,and then frontal precipitation turned up rapidly in the later stage of this event with surface cold air mass intrusion and southeast-moving of low-level shear line and high level trough.The short-time strong rainfall zone tallies well with the trend of the Nanling mountains,and extremely heavy rain is caused by several mesoscale convective systems(MCS)and topographic forcing effect.High-echo-centroid short-time strong rainfall,thunderstorm gales and big hailstone occurred mainly in the warm area precipitation stage.After the front passed over mountain,low-echo-centroid short-time strong rainfall occurred but thunderstorm gales and hailstone seldom occurred.(2)Mesocyclone,high vertically integrated liquid(V IL)value,overhang echo and BWER observed in the radar echo map can provide important indicative features for the early warning of big hailstone,in which midaltitude radial convergence(MARC)is the key feature for the alerts of thunderstorm gales.(3)Deep dry layer at upper levels and high humidity at lower levels are favorable to the generation of big hailstone,and strong vertical wind shear between 0 and 6 km is favorable to the enlargement of hailstone.The large value of downdraft convective available potential energy(DCAPE)is a reference index for the forecast of thunderstorm gales,and the total layer dew-point depression and the small value of DCAPE are the reference basis to judge the occurrence of only short-time strong rainfall.(4)Bell-mouthed and windward direction topographic effect in the Nanling Mountains and its surrounding areas is conductive to the convergence of air flow in the low-level that triggers convection,causing the large frequency of heavy rainfall and the long lasting of precipitation.The frontogenesis in leeward side of Nanling Mountains increases the possibility of thunderstorm gale,hail and other weather in the southern foot-hills of Nanling Mountains.