Fine Structure of the Breakthrough Phase of the Attachment Process in a Natural Lightning Flash

Abstract

The attachment process in cloud-to-ground lightning flashes is a crucial process that eventually switch on the discharge route between the cloud and the ground, acting as a transition from the leader stage with a peak current of 1-2 kA to the return stroke stage with a peak current of several tens of kiloamperes (Pu et al., 2019; Rakov & Tran, 2019). In response to the downward leaders starting from the charged clouds, upward connecting leaders (UCLs) of the opposite polarity are initiated from the grounded objects, extend their channels toward the approaching downward leader and make contact, followed by the collision and return stroke (Saba et al., 2017). The progress of the knowledge of lightning attachment experienced the identification of the existence of UCL at the early stage (Golde, 1967; Orville, 1968), later the investigation of the characteristics of the leaders that determine the connection point or influence the selection of contacted leaders (Jiang et al., 2015; Lu et al, 2013, 2016; Qie & Zhang, 2019), and more recently the exploring of the so called breakthrough phase (BTP) which is one of the most poorly understood processes in lightning physics (Tran & Rakov, 2017).

Observations of the Breakthrough Phase of Attachment Process in Laboratory Long Sparks

“…In three of these events (see Figure 2), luminous structures were observed inside the shrinking common streamer zones just before the return stroke frames. The luminous structures in Figures 2a and 2c features based on their appearance: the first one links the positive and negative leaders, similar to the weak luminous route linking the approaching leaders observed by Jiang et al (2021) in natural lightning, and the other is floating. Notably, luminous structures act as selected routes and eventually transformed into a part of the return stroke channel.…”

“…Kostinskiy et al (2016), for the first time, reported the evolution of the common streamer zone in meter-scale sparks generated by artificial clouds of negatively charged water droplets and estimated the speeds of the positive and negative leaders within it. Jiang et al (2021) reported a weak Abstract High-speed video frames and discharge current records of 34 long laboratory sparks were examined. Two consecutive frames of the breakthrough phase, depicting the evolution of the common streamer zone, were obtained in five events, all presented in this study.…”

“…In all the above cases, the common streamer zone was imaged in a single frame. Only two optical records of the breakthrough phase, reported by Kostinskiy et al (2016) and Jiang et al (2021), were imaged in two consecutive frames. Kostinskiy et al (2016), for the first time, reported the evolution of the common streamer zone in meter-scale sparks generated by artificial clouds of negatively charged water droplets and estimated the speeds of the positive and negative leaders within it.…”

“…Jiang et al. (2021) reported a weak luminous selected route linking downward and upward leaders that involved in the evolution of the breakthrough phase in natural lightning. They interpreted the conversion of the high‐impedance common streamer zone to a hot plasma channel as the dominant development of the selected route rather than the shrinking of the common streamer zone.…”

The Attachment Process of Negative Connecting Leader to the Lateral Surface of Downward Positive Leader in a Positive Cloud‐To‐Ground Lightning Flash

“…, leader connecting behavior (e.g., Lu et al, 2013Lu et al, , 2016, striking distance characteristics (e.g., Qi et al, 2021;Visacro et al, 2017b), and streamer zone structure (e.g., Jiang et al, 2021;Plaisir et al, 2023;Saba et al, 2022;Tran & Rakov, 2017).…”