Radial structure and optical radiation characteristics of the cloud-ground lightning channel
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摘要:
研究云地闪电通道的径向结构及光辐射特征，可为揭示云地闪电通道形成和发展过程的微观物理机制提供参考依据，为闪电防护提供科学指导。本课题组利用无狭缝高速摄谱仪，在青海高原地区实施野外观测试验。在一次云地闪电中记录到了清晰可见的通道核心，而且在通道核心的外边缘和外部发光通道之间发现一个较弱的发光区。基于光谱观测结果，对比分析了首次回击和第三次继后回击的光辐射特征。实验验证了闪电通道电晕鞘模型，确定了连接点的位置，估算得到两个回击的闪击距离分别为57 m和53 m，并证实了回击放电最强的点在连接点处。由此可推断，在回击初期，云地闪电回击通道沿径向由内到外依次为通道核心-弱发光区-电晕鞘外层，即闪电通道内沿通道径向的电荷分布是不均匀的，闪电通道的光辐射特征与放电强度和持续时间密切相关。
Abstract:The study of the radial structure and optical radiation characteristics of the cloud-ground lightning channel can provide a reference for the revealing of the microphysical mechanism of the formation and development of the cloud-ground lightning channel, and provide scientific guidance for the lightning protection. We carried out field observation experiments in the Qinghai Plateau region using a slit-less high-speed spectrograph. The clearly visible channel core was recorded in a cloud-ground lightning, and a weak luminescent region was found between the outer edge of the channel core and the external luminescent channel. Based on the spectral observation results, the optical radiation characteristics of the first return stroke and the third subsequent return stroke were compared and analyzed. The corona sheath model of the lightning channel is verified experimentally, the location of the connection point was determined, and the estimated striking distance of the two return strokes is 57 m and 53 m respectively, and the strongest point of the return discharge is confirmed at the connection point. It can be inferred that in the initial stage of the return stroke, the cloud ground lightning return stroke channel consists of the channel core , the weak luminescence region and the outer corona sheath from the inside to the outside, that is, the charge distribution along the radial direction of the lightning channel is uneven. The light radiation characteristics of lightning channel are closely related to the intensity and duration of discharge.
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Key words:
- lightning channel /
- radial structure /
- channel core /
- weak luminescent region /
- charge distribution
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图 1 梯级先导通道的最后一幅图片和首次回击通道的连续两幅图片
Figure 1. Last image of the stepped leader channel and the two successive images of the first return stroke channel. (a) −0.125 ms; (b) 0 ms; (c) 0.125 ms
图 2 不同样品点沿通道径向的灰度值分布
Figure 2. Gray value distribution of the different sample points along the radial channel
图 3 首次回击不同时刻的原始光谱图
Figure 3. Original spectrogram of the first return stroke at different times. (a) −0.125 ms; (b) 0 ms; (c) 0.125 ms
图 4 首次回击通道上4个样品点分别在0和0.125 ms的谱线图
Figure 4. Spectra of 4 sample points on the first return stroke channel at 0 and 0.125 ms, respectively
图 5 首次回击和第三次继后回击的通道图片
Figure 5. Channel images of the first return stroke and the third subsequent return stroke
图 6 第三次继后不同时刻的原始光谱图
Figure 6. Original spectrogram of the third subsequent return stroke at different times. (a) 87.013 ms; (b) 87.138 ms; (c) 87.263 ms
图 7 第三次继后回击4个样品点分别在87.138 ms的谱线图
Figure 7. Spectra of 4 sample points of the third subsequent return stroke at 87.138 ms
表 1 首次回击时观测到的谱线波长、激发能和跃迁几率
Table 1. Observed spectral line wavelengthes, excitation energies and transition probabilities in the first return stroke
波长 (nm) 激发能 (eV) 跃迁几率 (×108 s−1) NII 444.7 23.196 1.12 NII 463.0 21.159 0.748 NII 500.5 23.141 1.14 NII 568.0 20.665 0.496 NII 594.2 23.239 0.547 Hα 656.3 12.087 0.441 OI 715.6 14.460 0.505 NI 746.8 11.995 0.196 OI 777.4 10.740 0.369 OI 794.7 14.100 0.373 NI 821.6 11.844 0.226 OI 844.6 10.988 0.322 NI 868.0 11.763 0.253 
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