Characteristics of lightning leader propagation and ground attachment
Characteristics of lightning leader propagation and ground attachment
复制标题
闪电先导传播和接地特性
DOI：
10.1002/2015jd023519
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发表时间：
2015-12-16
影响因子：
4.4
通讯作者：
Li, Xun
中科院分区：
文献类型：
--
作者：
Jiang, Rubin;Qie, Xiushu;Li, Xun
利用高速摄像和时间相关电场变化对37次自然负闪的接地过程和先导行为进行了分析。在回击前的帧中，在下行先导尖端下方发现了弱发光接地通道，考虑到闪电附着的物理过程，推测其为上行连接先导，但序列帧并未直接证实。对于阶状先导先行回击，向上连接先导倾向于由那些亮度较亮、通道尖端较低的下行先导分支诱发，它们完成附着的可能性较大。在回击之前的帧中捕获了61个先导后续冲程序列中的2个的向上连接先导，分别表现出340 m和105 m的相对较长的通道长度。诱导向下的后继先导是混沌型的，其特征是持续时间为0.2- 0.3ms的不规则电场脉冲串。当发生附着时，阶梯状先导系统与地面之间的高电位差的瞬时下降将在宏观上终止那些未接地的分支的传播，而不会有效地阻止低电位中现有空间干系统的发展。电导率拖缆区与先导尖端分开。当不接地支路与主中风通道连接不良时，它们向地面的进一步传播是可行的。这两个因素可能会导致在同一个领导人回击序列中发生多个接地。
The grounding process and the associated leader behavior were analyzed by using high-speed video record and time-correlated electric field change for 37 natural negative cloud-to-ground flashes. Weak luminous grounded channel was recognized below the downward leader tip in the frame preceding the return stroke, which is inferred as upward connecting leader considering the physical process of lightning attachment, though not directly confirmed by sequential frames. For stepped leader-first return strokes, the upward connecting leaders tend to be induced by those downward leader branches with brighter luminosity and lower channel tip above ground, and they may accomplish the attachment with great possibility. The upward connecting leaders for 2 out of 61 leader-subsequent stroke sequences were captured in the frame prior to the return stroke, exhibiting relatively long channel lengths of 340 m and 105 m, respectively. The inducing downward subsequent leaders were of the chaotic type characterized by irregular electric field pulse train with duration of 0.2-0.3 ms. The transient drop of the high potential difference between stepped leader system and ground when the attachment occurred would macroscopically terminate the propagation of those ungrounded branches while would not effectively prevent the development of the existing space stem systems in the low-conductivity streamer zone apart from the leader tip. When the ungrounded branches are of poor connection with the main stroke channel, their further propagation toward ground would be feasible. These two factors may contribute to the occurrence of multiple grounding within the same leader-return stroke sequence.