Unique UV images of lightning leading to new insights into its propagation and attachment

Development of hot lightning channels is facilitated by essentially cold streamers emanating from their extremities. Negatively-charged channels extend intermittently, with each step culminating in a strong streamer burst. Thus, streamers play a crucial role in lightning, yet they are poorly understood, because they emit primarily ultraviolet (UV) light, which usually goes undetected. Here, we present unique UV images of both positive and negative streamers leading to new insights into the lightning propagation and attachment. A downward-extending negative channel induced a ~20-m long positively-charged hot channel developing from a roof-top vent pipe and having ~70-m long positive streamers emanating from its tip. The positive streamers extended toward the negative streamers of a descending-channel branch, as normally happens during the lightning attachment process. However, the expected attachment to the vent pipe failed, and ground connection occurred ~200 m away from it. This failure to connect to the vent pipe was likely due to the self-choking effect of the large negative space charge that was suddenly introduced by the step-related streamer burst ahead of the lower end of the descending channel. The observed abrupt change of the propagation path to ground has important implications for the validity of the traditional lightning protection concepts.

热雷电通道的发展过程，主要得益于其端部发射的冷流光（streamer）。带负电的通道呈间歇性延伸，每一次步进均以强烈的流光爆发收尾。由此可见，流光在雷电过程中发挥着关键作用，但人们对其认知仍较为匮乏——这是因为流光主要辐射紫外线（UV），通常难以被观测到。本研究展示了正负流光的独特紫外影像，为雷电传播与附着过程的研究带来了全新认知。一条向下延伸的负电通道，诱发了由屋顶通风管道生成的长约20米的正电热雷电通道，该通道的端部向外辐射出长约70米的正流光。正流光朝向下降通道分支的负流光方向延伸，这一现象与雷电附着过程中的常规表现一致。但预期中与通风管道的附着并未发生，最终接地位置距离该管道约200米。此次未能与通风管道实现有效连接，大概率是由于下降通道下端前方的步进相关流光爆发，突然引入了大量负空间电荷，进而引发了自阻塞效应。本次观测到的雷电向地传播路径的突变现象，对传统雷电防护理念的有效性具有重要的参考意义。