S-band and X-band Radar Observation Characteristics of EF2 Tornado at Qingyuan of Baoding in 2021
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摘要: 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。Abstract: 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 Donglü Village, 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 low-vortex 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.
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图 2 2021年7月21日08:00 500 hPa高度(蓝线,单位:hPa)、500 hPa温度(红虚线,单位:℃)和850 hPa风场(风羽) (a)及地面气压场(蓝线,单位:hPa) 和风场(风羽) (b)
Fig. 2 500 hPa geopotential height (the blue contour, unit: hPa), 500 hPa temperature (the red dashed line, unit: ℃) with 850 hPa wind (the barb) (a) and pressure (the blue contour, unit: hPa) with wind (the barb) at the surface(b) at 0800 BT 21 Jul 2021
图 3 2021年7月21日08:00—22日08:00清苑站物理要素时间-高度分布(填色为比湿,折线为垂直速度(单位:Pa·s-1),风羽为风场)
Fig. 3 Time-height section of physical elements at Qingyuan Station from 0800 BT 21 Jul to 0800 BT 22 Jul in 2021 (the shaded denotes specific humidity, the curve denotes vertical velocity(unit: Pa·s-1) and the barb denotes wind)
图 6 2021年7月21日15:48 SPOL和15:44 XPAR组合反射率因子及径向速度对比(a)SPOL组合反射率因子,(b)XPAR组合反射率因子,(c)SPOL 0.5°仰角径向速度,(d)XPAR 3.0°仰角径向速度
Fig. 6 Comparison of combined reflectivity factor and radial velocity of SPOL at 1548 BT and XPAR at 1544 BT on 21 Jul 2021(a)combined reflectivity factor of SPOL, (b)combined reflectivity factor of XPAR, (c)radial velocity at 0.5° elevation of SPOL, (d)radial velocity at 3.0° elevation of XPAR
图 8 2021年7月21日15:30—16:00 SPOL和XPAR探测龙卷风暴单体参数(a)最大反射率因子,(b)最大反射率因子所在高度,(c)垂直积分液态水含量,(d)回波顶高
Fig. 8 Tornado storm parameters of SPOL and XPAR from 1530 BT to 1600 BT on 21 Jul 2021(a)maximum reflectivity factor, (b)height of maximum reflectivity factor, (c)vertical integrated liquid water content, (d)echo top height
表 1 中气旋特征参数统计表
Table 1 Statistical table of characteristic parameters of mesocyclone
仰角/(°) 旋转速度/(m·s-1) 涡度/s-1 直径/km XPAR SPOL XPAR SPOL XPAR SPOL XPAR SPOL 0.0 0.5 12.8 11.0 12.4 10.4 4.8 4.7 1.5 1.5 13.2 11.1 13.0 9.1 4.9 5.1 3.0 2.4 13.8 8.8 12.0 8.0 5.3 4.6 4.5 3.4 13.6 7.1 12.2 9.3 5.3 3.8 6.0 4.3 13.6 8.3 10.5 8.5 6.1 3.6 7.5 6.0 12.5 5.8 11.6 3.8 5.2 5.8 -
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