2021年保定清苑EF2级龙卷S和X波段雷达特征

S-band and X-band Radar Observation Characteristics of EF2 Tornado at Qingyuan of Baoding in 2021

利用石家庄S波段天气雷达(SPOL)、雄安X波段相控阵雷达(XPAR)、地面自动气象站等多源观测资料,分析2021年7月21日河北省保定市清苑区东吕村EF2级龙卷雷达特征。清苑区龙卷发生于低涡降水云系中,风暴后向传播造成的多单体合并形成超级单体,钩状回波顶部分裂的强反射率因子核心自东南向西北移动,并与龙卷位置对应关系较好。SPOL和XPAR平均径向速度图上均连续多个时次识别出中气旋,中气旋尺度为1.4~4.2 km,旋转速度为10~20 m·s^(-1),为弱中气旋,属于微型超级单体龙卷,持续时间较短(30~35 min)。在龙卷发展演变过程中,低仰角探测到紧邻的旋转速度对时,中气旋向下延伸1.2~1.4 km,直径迅速收缩0.8~1 km,预示龙卷的发生。龙卷风暴在低层旋转速度和涡度最大,有利于龙卷发展增强。SPOL和XPAR在龙卷位置、径向速度及风暴直径的探测结果较为一致,XPAR回波顶比SPOL高约6 km,且XPAR回波顶的峰值时段与风暴出现冲云顶特征的时段一致。15:36—15:42(北京时)龙卷涡旋特征(TVS)最为强盛,垂直伸展厚度达2~4 km。

Using multiple observations such as S-band radar(SPOL)in Shijiazhuang,X-band phased array radar(XPAR)in Xiong’an,and ground-based encrypted automatic stations,detection features and evolutions of EF2 tornado at DonglüVillage,Qingyuan District of Baoding City Hebei Province on 21 July 2021 are studied.The tornado occurred within the center of high dew point values and in an area characterized by a significant temperature gradient.There are convergence lines within the center of high dew point temperatures and a temperature gradient zone.From perspectives of environmental conditions such as convective available potential energy(CAPE),0-6 km vertical wind shear,and the lifting condensation level(LCL),there is a possibility for tornado occurrence.It is evident that the tornado formed within a lowvortex precipitation cloud system,showing significant divergence at high altitudes.The subsequent storm propagation leads to multiple single-cell mergers and a supercell formation.A significant reflectivity factor core moving from southeast to northwest is observed at the top of hook echo,corresponding to the tornado location.Both SPOL and XPAR detected continuous mesocyclones on average radial velocity images,with dimensions ranging from 1.4 to 4.2 km,and rotating speeds of 10-20 m·s^(-1),indicating weak mesocyclones with short durations(30-35 min).During tornado development,a decrease in the lower angle detection of adjacent rotational speed pairs coincides with mesocyclone downward extension to 1.2-1.4 km and its diameter shrinking to 0.8-1 km,indicating tornado formation.Tornado storm parameters show maximum rotation speed and vorticity at low levels,promoting its intensification.Compared with XPAR storm parameters,SPOL features a larger maximum reflectivity factor(noless than 55 dBZ)and a greater distribution height(8-10 km).The consistency of SPOL and XPAR in detecting the tornado location,radial velocity,and storm diameter is compared.On the radar radial velocity image,there are pairs of positive and negative velocity values arranged symmetrically along the radial direction.The echo top of XPAR radar is approximately 6 km higher than that of SPOL radar,and the peak time of XPAR echo coincides with the storm’s appearance.The tornado vortex signature(TVS)reaches its strongest period from 1536 BT to 1542 BT,extending vertically up to 2-4 km.