Doppler Radar Characteristics and Cause Analysis of a Continuous Downburst in Zhejiang
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摘要: 利用常规高空、地面观测资料、ERA5再分析资料(0.25 °×0.25 °)、多普勒雷达产品对2020年3月21日浙江连续下击暴流的多普勒雷达特征及成因进行分析。(1) 此次过程发生在中高层西南急流、地面低压倒槽强烈发展的环流背景下，为低层暖平流强迫型强对流。整层大气湿层浅薄，近地面逆温和中层干冷增强了上干冷下暖湿的不稳定层结，高空强垂直风切变有利于强风暴的形成和发展，地面中尺度辐合线在高温背景下触发了此次过程。(2) 连续下击暴流由2个多单体风暴造成，两个风暴均呈现“弓形”特征，具有中层回波悬垂、有界弱回波区、三体散射等特征。单体K0中极端大风出现在最大反射率因子高度、风暴顶高、VIL下降阶段，而单体Y5中极端大风出现时风暴顶高、最大反射率因子高度、反射率因子核高度稳定少变。(3) 10级以上下击暴流主要出现在涡度平流强烈发展、中层有弱冷空气入侵阶段。单体K0中致灾下击暴流主要由冰雹的拖拽作用产生，而单体Y5中致灾下击暴流由冰雹和短时强降水共同的拖拽作用产生。Abstract: Using routine observation data, ERA5 hourly reanalysis data (0.25 ° × 0.25 °) and Doppler weather radars in Zhejiang Province, this paper analyzed the doppler radar characteristics and cause of the event that occurred on March 21, 2020. The results showed that: (1) This process occurred under the background of strong development of the southwest jet at the middle and upper levels and the surface low-pressure trough which was a forced strong convection of the low-level warm advection. The wet layer of the whole atmosphere was shallow, the near surface inversion and the middle dry cooling layer enhanced the unstable stratification with dry and cold upper and warm and wet lower, while the strong vertical wind shear in the upper air was conducive to the formation and development of strong storms, and the surface mesoscale convergence line triggered this process under the high temperature background. (2) The downburst was caused by two multi-cell storms exhibiting"Bow Echo"characteristics, including mid-level echo overhang, bounded weak echo zone, and three-body scattering. Extreme winds occurred during the descending phase of maximum reflectivity factor altitude, storm crest height, and VIL descent in unit K0, while the maximum reflectivity factor altitude, storm crest height, and reflectivity factor kernel remained relatively stable in unit Y5. (3) The downburst above level 10 primarily occurred during the stage of strong development of vorticity advection and weak cold air intrusion in the middle layer. The disaster-causing downburst in unit K0 was mainly generated by the dragging effect of hail, while in unit Y5, it was generated by the combined dragging effect of hail and short-term heavy precipitation.
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Key words:
- downburst /
- supercell /
- mesocyclone /
- ground convergence line
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图 2 3月21日14时500 hPa高度场(黑实线，单位：gpm)、700 hPa急流(红实线，单位：m·s-1)、850 hPa风场(风向杆，单位：m·s-1)(a，蓝实线为切变线)和地面气压场(黑实线，单位：hPa)、风场(风向杆，单位：m·s-1)(b，红实线为地面辐合线)
图 9 21日08—20时下击暴流区(120.00~121.25 °E、29.5~30.0 °N)涡度平流(a，单位：10-9s-2)、假相当位温平流(b，单位：10-4 K·s-1)、风场(风向杆，单位：m·s-1)垂直剖面
表 1 3月21日风暴单体Y5中气旋阶段不同时刻属性列表
时间 底高/km 顶高/km 最强切变高度/km 旋转速度/(m·s-1) 强度 径向距离/km 17:34 0.7 2.7 0.7 16 弱 59.4 17:40 0.6 2.7 0.6 19 中等 56.8 17:46 0.8 4.2 0.8 19 中等 65.2 17:51 2.2 4.4 2.2 14 弱 76.0 17:57 4.5 5.9 4.5 15 弱 72.7 
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