华南一次非中气旋海面龙卷的大气条件和雷达特征分析

ANALYSIS OF ATMOSPHERIC CONDITIONS AND RADAR CHARACTERISTICS OF A NON-MESOCYCLONE WATERSPOUT IN SOUTH CHINA

利用S波段双偏振雷达、风廓线雷达、L波段探空雷达、区域自动站等观测资料和ERA5再分析资料,对2019年5月26日发生在华南地区一次季风暴雨中海上龙卷过程的大气条件和雷达特征进行了详细分析。(1)低层辐合、高层辐散、中层短波槽东移的环流特征为龙卷的对流风暴提供了有利的大尺度动力抬升条件,与大多数陆龙卷的形成机制相似。(2)该龙卷形成的环境条件也与一般非中气旋陆龙卷近似,具有中等大小的对流有效位能,对流抑制能量接近0,为该对流风暴发生发展提供了热力条件,具有发生龙卷的潜势;强0~1km低层风垂直切变和0~6km深层风垂直切变为该对流风暴发展提供了动力条件,其中低层风垂直切变远高于过去对陆龙卷低层风垂直切变统计的下限。(3)雷达发现:龙卷出现前后,TVS(TornadicVortexSignature)雷达产品多次定位提醒,但中气旋产品并未有提醒,有一定示警作用;径向速度产品揭示了龙卷正负速度对的发展变化;龙卷低层旋转速度大值区多位于带状回波前沿,对应的差分反射率Z_(DR)减小,相关系数CC较低,有利于确定龙卷的持续时间和影响范围。

Using data from S-band dual-polarization radars,boundary layer wind profiler radars,and Lband sounding radars,observational data from automatic surface weather stations,and ERA5 reanalysis data,the present study analyzes the atmospheric conditions and radar characteristics of a waterspout on May 26,2019 in South China.The results show that:(1)Similar to the formation mechanism of most tornadoes,the low-level convergence,high-level divergence and eastward movement of the middle-level shortwave trough provided favorable conditions for the large-scale dynamic uplift of the convective storms of the waterspout.(2)The environmental conditions of the waterspout were also similar to those of general non-mesocyclone tornadoes.It had medium-sized convective available potential energy and its convective suppression energy was close to 0,providing thermal conditions for the occurrence and development of the convective storm.The strong 0~1 km low-level wind vertical shear and the 0~6 km deep-level wind vertical shear provided dynamic conditions for the development of the convective storm,and the low-level wind vertical shear was much higher than the previous statistical lower limit of the low-level wind vertical shear of land tornadoes.(3)Radar data shows that:(a)Tornadic vortex signature(TVS)has a certain warning effect as it reminded the location of the waterspout for many times,but the mesocyclone products did not.(b)Radial velocity product revealed the development of the positive and negative velocity pairs of the waterspout.(c)The large value area of the waterspout low-level rotation velocity was mostly located at the bow echo front,the corresponding differential reflectivity Z_(DR) decreased,and the correlation coefficient CC was low,which may help predict the duration and influence range of the waterspout.