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Initial Stage of Lightning Discharges Initiated by NBE and IBP
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摘要: 基于闪电低频电场探测阵列（LFEDA）所获得的全闪三维定位数据，研究了2015年8月15日14：30—16：10广州一次雷暴过程中具有明显始发脉冲的闪电初始放电特征及放电规律。结果表明：212例近距离云闪和地闪中，32例闪电由窄偶极性放电事件（NBE）始发，占15%；180例闪电由初始击穿脉冲（定义初始击穿脉冲簇的首个脉冲为FIBP）始发，占85%。作为始发的窄偶极性放电事件（INBE），其相对孤立且具有较大的相对幅度，INBE与后续闪电的第1个脉冲的时间间隔为7 ms，幅度比为3.5，远大于FIBP相对应的时间间隔0.6 ms和幅度比0.8，INBE后多跟随传统的IBP脉冲。多数正极性INBE与FIBP对应初始向上发展的闪电，而负极性对应初始向下发展的闪电。INBE始发闪电前15 ms的平均发展速度随始发高度的增大而减小，快于FIBP，这与INBE具有更快的速度相关。估计的INBE速度为4.7×107 m·s-1，FIBP速度为1.5×107 m·s-1，两者速度差异也体现在脉冲上升时间方面，INBE具有更快的上升沿。Abstract: Lightning initial stage is an important and fundamental physical process. How lightning initiates is a hot topics in the research of lightning physics. Initial breakdown is observed by many researchers, and the first pulse of IBP is regarded as the starting marker of intracloud lightning or cloud-to-ground lighting. Lightning discharge characteristics and laws during initial stage in a thunderstorm progress are researched based on Low-frequency E-field Detection Array (LFEDA). In 212 intracloud lightnings and cloud-to-ground lightnings of short range, 32 lightnings are initiated by NBE, accounting for 15%, and 180 lightnings are initiated by IBP, accounting for 85%. As an initial NBE (INBE), it is more isolated and larger than the first pulse of initial IBP (FIBP). The average time interval from INBE to subsequent first pulse is 7 ms, with a mid-value of 3.9 ms. The amplitude ratio between INBE and the subsequent pulse is 3.5. The above values are larger than those of FIBP with the corresponding values of 0.6 ms, 0.2 ms and 0.8. Most of the positive INBE and FIBP corresponds to an upward discharge in the initial stage while negative correspond to a downward one. The average height of INBE is 9.9 km, which is less than isolated NBE of 13.6 km. There is also a sensible difference in discharge height between isolated positive NBE and the negative one. The isolated negative NBE is much higher than the positive one. It may occur between upper positive charge region and shielding layer, which is related to the middle and upper atmosphere discharge. The average height of FIBP is 8.1 km. There are no obvious differences in discharge height between INBE and FIBP. The average speed during the first 15 ms of the lightning initiated by NBE is 3.1×105 m·s-1, with a mid-value of 3.0×105 m·s-1, which decreases with the initial altitude. The maximum and minimum average speed is 7×105 m·s-1 and 1.2×105 m·s-1, respectively. To better reveal the difference in INBE and FIBP, an estimated velocity is calculated based on the hypothesis of low-frequency pulse corresponding to a channel extending. The estimated speed of INBE is 4.7×107 m·s-1, which is faster than FIBP with a velocity of 1.5×107 m·s-1. The shorter rising time for INBE also indicates a faster velocity. There are no apparent differences in rising time, half-peak width and pulse width for INBE, NBE in process and isolated NBE. It is difficult to distinguish INBE from other NBE by pulse property.
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Key words:
- NBE;
- IBP;
- lightning initiation
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图 1 LFEDA站网子站分布
(阴影表示地形高度)
Fig. 1 Substation distribution of LFEDA network
(the shaded denotes the topography)
图 2 典型闪电始发放电事件
(a)NBE，(b)云闪IBP，(c)地闪IBP
Fig. 2 Typical lightning initial discharge events
(a)NBE, (b)IBP waveform during intracloud lightning, (c)IBP waveform during and cloud-to-ground lightning flash
图 3 闪电始发过程个例(▲表示始发放电事件)
(a)正极性NBE始发过程，(b)负极性NBE始发过程，(c)正极性IBP始发过程，(d)负极性IBP始发过程
Fig. 3 Lingtning initial progress(▲ denotes initial discharge events)
(a)positive NBE initial progress, (b)negative NBE initial progress, (c)positive IBP initial progress, (d)positive IBP initial progress
图 4 各类型闪电初始高度分布特征
(a)INBE，FIBP，过程中NBE，(b)正极性FIBP和负极性FIBP，(c)过程中正极性NBE和过程中负极性NBE，(d)孤立正极性NBE和孤立负极性NBE
Fig. 4 Distribution characteristics of initial altitude for all-type lightning
(a)initial NBE, initial IBP, intra-NBE, (b)positive and negative initial IBP, (c)positive and negative intra-NBE, (d)positive and negative isolated NBE
图 5 闪电初始放电速度
(a)INBE初始高度与15 ms始发平均速度的关系，(b)INBE与FIBP始发闪电初始阶段速度分布对比
Fig. 5 Initial discharge speed of lightning
(a)relationship between INBE altitude and speed during initial 15 ms stage, (b)comparison for initial velocity distribution of initial stage by INBE and FIBP
表 1 闪电始发放电事件类型
Table 1 Types of initial lightning discharge events
样本极性 云闪INBE 云闪FIBP 地闪INBE 地闪FIBP 正极性 21 144 1 2 负极性 8 29 2 5 
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表 2 闪电始发放电事件发展方向统计
Table 2 Initial propagation direction of lightning discharge events
闪电类型 始发类型 个例数量 向上发展 向下发展 云闪 正极性INBE 21 20 1 负极性INBE 8 0 8 正极性FIBP 143 137 6 负极性FIBP 30 7 23 地闪 正极性INBE 1 1 0 负极性INBE 2 0 2 正极性FIBP 2 2 0 负极性FIBP 5 1 4
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表 3 INBE与FIBP脉冲参数对比
Table 3 Parameters comparing between INBE and FIBP
参数 特征量 INBE FIBP 正极性 负极性 正极性 负极性 上升时间/μs 平均值 1.3 1.2 3.9 4.0 最大值 3.7 2.2 12.4 11.3 标准差 0.8 0.5 2.9 3.0 半峰宽/μs 平均值 3.0 1.6 2.3 2.9 最大值 7.8 3.2 9.0 8.2 标准差 2.0 0.8 1.8 1.8 脉冲宽度/μs 平均值 4.6 4.0 6.5 6.3 最大值 8.1 6.3 8.1 8.1 标准差 1.8 1.4 1.1 1.3
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表 4 不同NBE脉冲波形参数对比
Table 4 Pulse waveform parameters comparing among different NBE
统计参数 特征量 INBE NBE 孤立NBE 正极性 负极性 正极性 负极性 正极性 负极性 上升时间/μs 平均值 1.3 1.2 1.4 1.3 1.4 1.1 最大值 3.7 2.2 4.0 3.1 7.2 2.1 标准差 0.8 0.5 1.0 0.6 1.2 0.4 半峰宽/μs 平均值 3.0 1.6 2.0 1.8 2.0 2.1 最大值 7.8 3.2 5.3 3.7 5.3 3.9 标准差 2.0 0.8 1.2 0.8 1.1 1.0 脉冲宽度/μs 平均值 4.6 4.0 4.1 4.2 4.2 3.9 最大值 8.1 6.3 8.1 6.7 8.1 5.5 标准差 1.8 1.4 1.6 1.1 1.4 1.0
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