Relationship between Lightning Activities and Radar Echoes of Squall Line Convective Systems
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摘要: 基于北京宽频带闪电网(Beijing Broadband Lightning Network,简称BLNet)获得的全闪三维定位和多普勒天气雷达等资料,详细分析了2015~2017年北京暖季7次强飑线过程的闪电活动与雷达回波强度之间的关系。结果表明,闪电主要发生于前部线状对流云区内且集中分布在30 dBZ以上的强回波区域,少部分的闪电分布在后部的层状云区域内。从闪电辐射源三维分布结构可以发现,闪电活动大部分处在6~11 km的高度范围。将能够同时反映强回波深度和面积的0~−30°C温度区域内大于30 dBZ雷达回波体积(V30dBZ)作为强回波指标,并与闪电活动进行统计分析发现,整体上在7次飑线过程中,总闪频数和V30dBZ存在较好的相关性,其中5次过程的闪电频数峰值同时或提前于V30dBZ的峰值出现,二者的时滞相关系数超过0.61,提前时间为0~96 min。另外两次过程中闪电峰值落后于V30dBZ峰值,落后时间分别为30 min和60 min。研究结果不仅对认识闪电与对流活动的关系有重要的科学意义,也可为闪电资料在数值模式中的同化应用提供科学依据。
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关键词:
- 飑线 /
- 闪电活动 /
- 大于30 dBZ雷达回波体积 /
- 滞后相关
Abstract: The relationships between the lightning activities and the radar reflectivity intensities of seven severe squall lines, which occurred in Beijing from 2015 to 2017, were analyzed. The analysis was done based on three-dimensional lightning location data from Beijing Broadband Lightning Network (BLNet) and the S-band Doppler radar. The results show that lightning flashes are mainly located in the convective leading line and centered in the strong echo region, with reflectivity greater than 30 dBZ, and a small part of lightning flashes distributed in the trailing stratiform region. Based on the three-dimensional lightning structure, the lightning flashes are mostly concentrated in the range of 6–11 km height layer. Using the radar echo volume with reflectivity >30 dBZ (V30dBZ) between the 0 and −30°C level, as a strong convection index to reflect both the depth and area of strong convection, we found that of all seven squall lines, the trend of the lightning frequency and V30dBZ evolution showed some relationship. For five squall lines, the lightning frequency peak is the same or earlier than that of V30dBZ, the lagged correlation coefficient is higher than 0.61, and the lightning frequency is earlier than V30dBZ, with a leading time from 0 to 96 min. For the other two cases, the lightning frequency peak lags V30dBZ at 30 and 60 min, respectively. The results are significant for understanding lightning activity and convection intensification and provide a scientific basis for lightning data assimilation in numerical weather prediction. -
图 1 北京宽频带闪电网(BLNet)的测站布局,测站如图中16个黑色三角形所示,红色边界为北京地区范围,绿色区域边界为河北区域范围,蓝色边界为天津区域范围
Figure 1. Layout of the Beijing Broadband Lightning Network (BLNet) with 16 stations (black triangles), the red line representing the Beijing area, the green line representing the Hebei area, and the blue line representing the Tianjin area
图 2 2017年7月7日第一次飑线过程(a)12:36、(b)13:12、(c)13:48和第二次飑线过程(d)14:48、(e)15:36、(f)16:24的S波段雷达组合反射率(单位:dBZ)与6 min内闪电活动分布;(g)第一次飑线12:54的雷达组合反射率,(h)沿图(g)中黑色虚线的垂直剖面,叠加剖线前后0.1°范围、6 min内的全部闪电辐射源(黑点)分布。(a)至(g)图中黑色点代表云闪(IC),蓝色“–”代表负地闪(NCG),黑色“+”代表正地闪(PCG)
Figure 2. Composite reflectivity from the S-band radar and corresponding lightning distributions within 6 min of the squall line (SL) on July 7, 2017: (a) 1236 UTC, (b) 1312 UTC, (c) 1348 UTC represent the first process (SL1); (d) 1442 UTC, (e) 1536 UTC, (f) 1624 UTC represent the second process (SL2). (g) The radar reflectivity of 1254 UTC for the first process; (h) the vertical cross-section of radar reflectivity along the dotted line shown in (g) and the lightning radiation sources (black dots) within 0.1° in 6 minutes. From (a) to (g), the black points represent IC (Intra-Cloud); the blue “–” represents NCG (Negative Cloud-to-Ground); the black “+” represents PCG (Positive Cloud-to-Ground)
图 3 2017年7月7日飑线过程中闪电频数和0~−30°C温度区域回波体积(V30dBZ和V35dBZ)随时间变化曲线:(a)地闪(CG)和云闪(IC);(b)正地闪(PCG)、负地闪(NCG)及正地闪比例(PCG/CG);(c)总闪频数[实线,单位:flashes (6 min)−1]和回波体积(虚线,V30dBZ和V35dBZ,单位:km3)
Figure 3. Evolution of lightning frequency of the squall line on July 7, 2017: (a) Cloud-to-ground (CG) and Intra-cloud (IC); (b) Positive CG (PCG), Negative CG (NCG) and the ratio of PCG (PCG/CG); (c) total lightning frequency [solid line, units: flashes (6 min)−1], and the echo volume greater than 30 dBZ, 35 dBZ between 0 and –30°C level (dotted lines, V30dBZ, V35dBZ, units: km3)
表 1 2015~2017年中7次飑线过程情况
Table 1. Overview of the seven squall line cases from 2015 to 2017
个例 时间
(协调世界时)平均闪电频数
/flashes (6 min)−1最大闪电频数
/flashes (6 min)−1天气系统背景条件
(500 hPa)20150727 08:00~13:36 284.2 1256 东北冷涡系统 20160609 07:00~23:12 35.3 118 槽前 20160621 08:00~14:54 85.8 429 槽前 20170707 11:30~16:48 95.2 416 东北冷涡系统 20170713 10:00~19:36 115.1 617 槽前 20170802 09:48~20:06 8.5 96 槽前 20170808 09:42~19:54 51.2 328 东北冷涡系统 表 2 2015~2017年飑线过程的时滞相关性分析
Table 2. Lagged correlation of the squall lines from 2015 to 2017
个例 闪电频数与V30dBZ
时
滞关系最大相关
系数(r)时间差/min 20150727 滞后 0.80 30 20160609 同期 0.68 0 20160621 滞后 0.58 60 20170707 同期 0.72 0 20170713 超前 0.69 6 20170802 超前 0.71 96 20170808 超前 0.69 6 -
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