A study of the ground-attachment process in natural lightning with emphasis on its breakthrough phase.
A study of the ground-attachment process in natural lightning with emphasis on its breakthrough phase.
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DOI：
10.1038/s41598-017-14842-7
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发表时间：
2017-11-17
影响因子：
4.6
通讯作者：
Rakov VA
中科院分区：
文献类型：
--
作者：
Tran MD;Rakov VA
在佛罗里达盖恩斯维尔的闪电观测站，获得了4次自然闪电中的负击的同步高速（124或210千帧/秒）视频图像和附着过程的宽带电磁场记录。大多数图像向上连接的领导人（UCL）和向上不连接的领导人，推断主要是从树木发起，表现出脉动的行为（增亮/褪色周期）。UCL在空气中的传播速度为1.8 × 105 ~ 6.0 × 105 m/s，平均为3.4 × 105 m/s，最大传播距离为11 ~ 25 m。在距地面100 m范围内，负先导与正UCL的速度比，有2次约为3-4，有1次约为0.5。对2个事件的突破阶段（最终跳跃）进行成像。共同拖缆区（CSZ）的初始长度估计约为30-40 m。在2个事件中，正、负先导在CSZ内相互发展的速度在2.4 × 106 ~ 3.7 × 106 m/s之间。对于1起事件，观察到相反极性先导在CSZ内加速。突破阶段结束时的电流平均持续4.7 μs，估计约为总电流峰值的一半，因此，传统上归因于返回冲程过程的电流峰值的一半实际上与两个先导在CSZ内相互延伸碰撞有关。
Synchronized high-speed (124 or 210 kiloframes per second) video images and wideband electromagnetic field records of the attachment process were obtained for 4 negative strokes in natural lightning at the Lightning Observatory in Gainesville, Florida. The majority of imaged upward connecting leaders (UCLs) and upward unconnected leaders, inferred to be mostly initiated from trees, exhibited a pulsating behavior (brightening/fading cycles). UCLs, whose maximum extent ranged from 11 to 25 m, propagated in virgin air at speeds ranging from 1.8 × 105 to 6.0 × 105 m/s with a mean of 3.4 × 105 m/s. Within about 100 m of the ground, the ratio of speeds of the downward negative leader and the corresponding positive UCL was about 3–4 for 2 events and 0.5 for 1 event. The breakthrough phase (final jump) was imaged for 2 events. The initial length of the common streamer zone (CSZ) was estimated to be about 30–40 m. For 2 events, speeds of positive and negative leaders developing toward each other inside the CSZ were found to be between 2.4 × 106 and 3.7 × 106 m/s. For 1 event, opposite polarity leaders were observed to accelerate inside the CSZ. The current at the end of the breakthrough phase, lasting on average 4.7 μs, was estimated to be approximately one-half of the overall current peak. Thus, about one-half of the current peak traditionally attributed to the return-stroke process is actually associated with two leaders extending toward each other to collision inside the CSZ.
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