基于雷达观测的2021年6月珠江口一次水龙卷过程分析

ANALYSIS OF A JUNE 2021 WATERSPOUT IN THE PEARL RIVER ESTUARY BASED ON TWO DUAL POLARIZATION RADARs

利用常规地面和探空资料、珠海S波段双偏振多普勒天气雷达和珠海横琴X波段相控阵雷达资料对2021年6月1日发生在珠江口的水龙卷过程进行分析。研究表明:此次水龙卷过程发生在高层强辐散、中层短波槽影响、低层西南风的背景场下;极低的抬升凝结高度、较大的0~1 km风矢量差、超过超级单体发生阈值的风暴相对螺旋度,为龙卷的发生提供了较好的动力条件。两部雷达均观测到超级单体结构特征,最强反射率因子超过65 d BZ。X波段相控阵雷达资料能够清晰展现水龙卷超级单体风暴精细化演变特征,0.9°仰角首先出现风切变,随后风切变出现高度逐渐增高,并加强为中气旋,切变最高高度达到17.1°仰角,随后高度逐渐降低,龙卷减弱。三维反射率因子图清楚地反映了龙卷母体风暴穹窿结构形成过程,以及强反射率因子区向上延伸,变细加强,龙卷触及水面后变粗的过程。S波段雷达探测到在龙卷发生前,出现ZDR低值眼区和ρHV弧,这对于预报员提前预警以及识别龙卷具有一定帮助。

Based on conventional observation and radiosonde data,an S-band dual polarization Doppler in Zhuhai and an X-band polarimetric phased array radar in Hengqin,Zhuhai,a waterspout that occurred in the Pearl River estuary on 1 June 2021 was analyzed.The results are shown as follows.The waterspout occurred under the background of strong high-level divergence,coupled with a shortwave trough in the middle level and a southwest air flow at the low level.The genesis of the waterspout was dynamically made possible as there were extremely low levels of lifting and condensation,a large wind vector difference in the 0-to-1 km layer,and a large storm relative helicity that was more than the threshold for supercell occurrence.Both of the radars observed the characteristics of supercells with the strongest reflectivity factor over 65 d BZ.The X-band polarimetric phased array radar well revealed the refined evolution process of the waterspout supercell.A weak wind shear was first detected at the 0.9°elevation,and then it occurred at increasing altitudes till it intensified to a mesocyclone.The wind shear reached the maximum height of 17.1°in elevation before it descended gradually while the waterspout weakened.A three-dimensional chart clearly shows how a dome structure developed in the parent storm body of the waterspout and a strong reflectivity column extended upward,contracted rapidly and intensified,as the waterspout touched down on the water surface before getting thicker in diameter.A low ZDReye and a ρHVarc were detected by the S-band dual polarization Doppler,which can be helpful for forecasters to issue warnings and identify the presence of tornadoes.