Lightning Activity of a Severe Thunderstorm with Several Hail-Fall Stages in Beijing Metropolitan Region
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摘要: 受东北冷涡和低层暖湿气流影响,2016年6月10日北京午后爆发了相继5次降冰雹的一次强雷暴天气过程。利用国家“973”项目“雷电重大灾害天气系统的动力—微物理—电过程和成灾机理(雷暴973)”2016年夏季协同观测期间获得的闪电全闪三维定位和多普勒天气雷达等资料,详细分析了此次雹暴的闪电活动和雷达回波特征。此次雹暴过程包括三个孤立的单体相继发展、并合,所分析的4次降雹过程中,总闪电频数在降雹期间都有明显增多,最高可达179 flashes min?1。云闪占全部闪电的80%以上,其中3次降雹前出现正地闪突增,其比例升高,占全部地闪的比例最高达58%。降雹时雷达回波>45 dBZ的面积增大,顶高超过13 km。整个雹暴过程,闪电辐射源主要分布在6~10 km的高度区域,与强回波具有一致性。所分析的4次降雹过程均出现明显的总闪频数跃增,并通过2σ阈值检验,其中3次提前时间为8~18 min,说明总闪频数对于降雹过程有一定的预警能力。Abstract: Influenced by the Northeast China cold vortex and warm-moist airflow in low level, a damaging thunderstorm with five hail-fall stages occurred in Beijing on 10 June 2016. Based on the 3D-location results of total lightning from Beijing Lightning Network (BLNET) and Doppler radar data during the STORM 973 (Dynamic–microphysical–electrical Processes in Severe Thunderstorms and Lightning Hazards) campaign in 2016, the characteristics of lightning activity and radar reflectivity structure during this thunderstorm were analyzed. The thunderstorm consisted of three isolated cells triggered in sequence and finally merged together. The total lightning frequency increased significantly during the four analyzed hail-fall stages, up to 179 flashes min?1. IC (intra-cloud) lightning flashes accounted for more than 80% of the total lightning. The ratio of PCG (positive cloud-to-ground) to CG (cloud-to-ground) lightning (PCG/CG) increased sharply before three hail-fall stages, by up to 58%. During the hailstorm developments, the area of radar echo greater than 45 dBZ increased, and the echo top exceeded 13 km. Lightning radiation sources mainly distributed in the altitude layer from 6 km to 10 km throughout the hailstorm process, which was consistent with a strong radar echo region. Moreover, the total lightning flashes increased dramatically before the three analyzed processes and passed the 2σ threshold test. Three of them were 8–18 minutes ahead of the hail-fallings, which shows that the total lightning frequency has a certain early warning ability for hail-fall processes.
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图 1 2016年6月10日08时(北京市,下同)(a)500 hPa等高线(黑线,单位:dagpm)、温度(填色,单位:°C)和风矢量(箭头,单位:m s−1),(b)850 hPa等高线(黑线,单位:dagpm)、比湿(填色,单位:g kg−1)和风矢量(箭头,单位:m s−1)
Figure 1. (a) 500-hPa geopotential height (black lines, units: dagpm), temperature (shadings, units: °C), and wind vectors (arrows, units: m s−1), (b) 850-hPa geopotential height (black lines, units: dagpm), specific humidity (shadings, units: g kg−1), and wind vectors (arrows, units: m s−1) at 0800 BJT (Beijing time) on 10 June 2016
图 2 2016年6月10日(a)08时、(b)20时北京站探空廓线。黑色实线表示温度,蓝色实线表示露点温度,红色虚线表示状态曲线
Figure 2. Sounding profiles for Beijing station at (a) 0800 BJT and (b) 2000 BJT on 10 June 2016. The black solid lines represent temperature, blue solid lines represent dew point temperature, and red dashed line represents parcel adiabatic lapse rate
图 3 2016年6月10日发生于北京地区一次雹暴过程中(a)地闪(CG)、云闪(IC)频数[单位:flashes (6 min)−1],(b)正(PCG)、负地闪(NCG)频数[单位:flashes (6 min)−1,左侧纵坐标]及正地闪比例(PCG/CG,右侧纵坐标表示每20 min正地闪数占总地闪数的百分比),(c)辐射源密度(填色,单位:pulses (0.5 km 6 min)−1),40 dBZ(虚线)、50 dBZ(实线)回波顶高度(单位:km)随时间的变化
Figure 3. Time evolution of (a) lightning frequency [units: flashes (6 min)−1] of IC (intra-cloud) and CG (cloud to ground) lightning flashes, (b) lightning frequency [units: flashes (6 min)−1, left y-axis] of PCG (positive cloud to ground), NCG (negative cloud to ground) lightning flashes and percentage of PCG (PCG/CG), the right y-axis represents the percentage of PCG to CG per 20 min, (c) lightning radiation source density [shadings, units: pulses (0.5 km 6 min)−1] and height (units: km) of echo tops for 40 dBZ (dashed line) and 50 dBZ (solid line) during the hailstorm generated in Beijing region on 10 June 2016
图 4 2016年6月10日(a)15时、(b)16时、(c)17时、(d)18时云顶亮温(填色,单位:°C)、30 dBZ雷达组合反射率(绿色等值线)与前后6 min内闪电分布(黑色“·”为云闪,深蓝色“×”为正地闪,浅蓝色“×”为负地闪)
Figure 4. TBB (black body temperature, shadings, units: °C), 30-dBZ composite reflectivity (green contours), and corresponding lightning (IC: black “·”; PCG: dark blue “×”; NCG: light blue “×”) in the preceding and following 6 min at (a) 1500 BJT, (b) 1600 BJT, (c) 1700 BJT, (d) 1800 BJT on 10 June 2016
图 5 2016年6月10日(a)15:24、(b)16:00、(c)16:54、(d)17:30四次降雹阶段的雷达组合反射率(填色,单位:dBZ)与前后6 min内的闪电分布(黑色“·”)。A、B、C为对流单体
Figure 5. Composite reflectivity (shadings, units: dBZ) at four hail-falling stages and distribution of lightnings (black “·”) in the preceding and following 6 min at (a) 1524 BJT, (b) 1600 BJT, (c) 1654 BJT, (d) 1730 BJT on 10 June 2016. A, B, and C represent different convective cells
图 6 沿图5中线段做剖面的雷达反射率(填色,单位:dBZ)与前后6 min内剖线±0.1°范围内的闪电辐射源(“·”)
Figure 6. Cross sections of radar reflectivity (shadings, units: dBZ) along lines in Fig. 5 and distribution of corresponding lightning radiation sources (black “·”) in the preceding and following 6 min and within ±0.1° of the lines shown in Fig. 5
图 7 2016年6月10日发生于北京地区一次雹暴过程中总闪频数(右侧纵坐标,蓝色线,单位:flashes (2 min)−1)、总闪频数的时间变化率(左侧纵坐标,柱状,单位:flashes (2 min)−2)、跃增阈值(左侧纵坐标,黑色线,单位:flashes (2 min)−2)
Figure 7. Total lightning frequency (right y-axis, blue line, units: flashes (2 min)−1), change rate of total lightning frequency (left y-axis, bars, units: flashes (2 min)−2), and jump threshold (left y-axis, black line, units: flashes (2 min)−2) during the hailstorm generated in Beijing region on 10 June 2016
表 1 不同降雹过程的降雹时间、总闪跃增时刻以及总闪频数超前时间
Table 1. Time of hail-falling, total lightning jump, and advance of total lightning frequency in different hail-fall processes
降雹过程 降雹时间 总闪跃增 超前时间/min 2 15:18~15:30 15:06 12 3 16:00~16:06 15:42 18 4 16:54~17:00 未通过阈值检验 5 17:24~17:36 17:16 8 -
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