2022年6月19日广东佛山龙卷的双极化相控阵雷达特征

Observation of the 19 June 2022 Tornado by X-Band Polarimetric Phased Array Radar in Foshan,Guangdong

利用X波段双极化相控阵雷达等多源观测资料,分析了2022年6月19日早晨广东佛山超级单体龙卷的环境条件和对流风暴的结构及演变特征。龙卷母体风暴是在强西南季风天气背景下的一条东北-西南向飑线南端发展起来的。环境条件具备较大对流有效位能、低抬升凝结高度和强垂直风切变等有利于超级单体龙卷发生发展的热力和动力条件;低空风暴相对螺旋度、超级单体复合指数和强龙卷指数的显著增强对超级单体龙卷的发生有较好指示意义。具有高时空分辨率的佛山南海X波段双极化相控阵雷达探测到了龙卷母体微型超级单体的发展过程和龙卷涡旋的演变特征:对流单体在前侧低层入流的加强下逐渐形成钩状回波和反射率弱回波空洞;中气旋首先在2.5 km附近高度形成后向低层伸展,随着后侧下沉气流的加强,低层涡旋旋转增强,当低层中气旋旋转速度超过22 m·s^(-1)(强中气旋)且直径紧缩至1.5 km以内时,龙卷即将触地,龙卷涡旋特征(TVS)和龙卷碎片特征(TDS)出现是龙卷触地的主要特征,龙卷发生在反射率弱回波空洞、TVS和TDS附近。

Based on the data of an X-band polarimetric phased array radar and other multi-source observation data,we present in detail the environmental conditions and evolution of the radar signatures of an EF1 tornado that took place in Foshan,Guangdong on 19 June 2022.The tornado was spawned from a supercell that developed at the southern end of a squall line,which developed in an active southwesterly airflow environment after the onset of the southwest monsoon.The ambient atmosphere had all thermal and dynamic conditions that were conducive to the occurrence and development of supercell and tornado,such as strong convective instability energy,low lifting condensation level and strong vertical wind shear.The significant enhancement of the low-level storm relative helicity,supercell composite parameter and significant tornado parameter had a good indication for the occurrence of a supercell tornado.A polarimetric phased array radar with high spatial and temporal resolution at Nanhai detected the development process of a mini-supercell and the evolution characteristics of a tornado vortex.The convective storm gradually formed a hook echo and a reflectivity hole with the strengthening of a front low-level inflow.The mesocyclone formed at a height of more than 2.5 km and then extended to the lower level.With the strengthening of rear-flank downdrafts,the vortex rotation at the lower level was enhanced.When the rotation speed of the low-level mesocyclone exceeded 22 m·s^(-1)(strong mesocyclone)and the diameter contracted to less than 1.5 km,the tornado was about to touch the ground.The appearance of tornado vortex signature(TVS)and tornadic debris signature(TDS)is the main feature of tornado occurrence.The tornado occurred near the reflectivity hole,TVS and TDS.