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.

热闪电通道的发展，主要由其末端产生的近乎冷态的流光（streamer）所驱动。带负电的通道呈间歇性延伸，每一次步进均以一次强烈的流光爆发收尾。因此，流光在闪电过程中发挥着关键作用，但由于其主要辐射紫外线（UV）且通常难以被探测到，人类对其认知仍十分有限。本研究通过获取正负流光的独有紫外线成像数据，为闪电传播与附着过程带来了全新的认知视角。一条向下延伸的负电通道，诱使一根屋顶通风管处产生了一条长约20米的带正电热通道，该通道末端向外辐射出长约70米的正流光。正流光朝着下行通道分支的负流光方向延伸，这正是闪电附着过程中的典型现象。然而，预期中应发生在通风管处的附着并未出现，最终的接地位置却距其约200米远。此次未能在通风管处完成接地，大概率是因为下行通道下端前方、由步进相关流光爆发突然引入的大量负空间电荷产生了自阻塞效应。本次观测到的闪电传播路径向接地位置的突变现象，对传统防雷理念的有效性具有重要的启示意义。