Close View of the Lightning Attachment Process Unveils the Streamer Zone Fine Structure

Abstract

A very close high‐speed video observation of lightning attachment to a building revealed novel details regarding the leader streamer zone dynamics. Upward leaders propagate in a steady and unbranched manner, displaying a uniformly luminous corona brush. The exception being the upward connecting leader (UCL) just before connection, when its streamer zone increases in size and develops a more filamentary pattern. Downward negative leaders have 3‐m long multiple streamers emanating from each negative leader tip. On some occasions, plasma formations known as space stems are seen to form in the location previously occupied by negative streamers. Space stems have luminosities comparable to the main leader channel, but are detached from it by 4 m. Some space stems display streamers of their own, including cases where streamers are emanating from both ends. The space stem formation hampered the propagation of the negative leader that was closest to the UCL.

Upward Leaders Initiated From Instrumented Lightning Rods During the Approach of a Downward Leader in a Cloud‐To‐Ground Flash

“…The downward leader that connected to leader B had also a constant speed but 2.0 times higher ( V d = 28.5 × 10 4 m/s) than the speed of leader B (similar to the speed reported by Visacro et al. (2017a, 2017b) for four natural downward leaders before attachment and similar to the speed of the branches analyzed separately in Saba et al., 2022). This confirms what was found for other cases of attachment process in the same buildings by Saba et al.…”

“…The downward leader that connected to leader B had also a constant speed but 2.0 times higher (V d = 28.5 × 10 4 m/s) than the speed of leader B (similar to the speed reported by Visacro et al (2017aVisacro et al ( , 2017b for four natural downward leaders before attachment and similar to the speed of the branches analyzed separately in Saba et al, 2022). This confirms what was found for other cases of attachment process in the same buildings by Saba et al (2017) and similar buildings in Saba et al (2022), that is, that contrary to what is observed in taller structures (Lu et al, 2013(Lu et al, , 2015 and assumed in some leader propagation models (Rizk, 1990(Rizk, , 1994, speeds are approximately constant, and the speed of the downward leader is higher than the speed of the upward leaders (speed ratio between 2.0 and 5.5). Table S1 in Supporting Information S1 compares the speeds, speed ratios and other important characteristics for the case analyzed in this work with three other attachment processes in the same building as reported by Saba et al (2017).…”

“…(2017) and similar buildings in Saba et al. (2022), that is, that contrary to what is observed in taller structures (Lu et al., 2013, 2015) and assumed in some leader propagation models (Rizk, 1990, 1994), speeds are approximately constant, and the speed of the downward leader is higher than the speed of the upward leaders (speed ratio between 2.0 and 5.5). Table S1 in Supporting Information compares the speeds, speed ratios and other important characteristics for the case analyzed in this work with three other attachment processes in the same building as reported by Saba et al.…”

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

“…The 2-D speed of NCL increases from 2.2 × 10 5 to 12.8 × 10 5 m/s (by a factor of 5.8), with an average of 7.3 × 10 5 m/s, and the 3-D speed of NCL increases from 2.2 × 10 5 to 15.3 × 10 5 m/s (by a factor of 7.0), with an average of 8.5 × 10 5 m/s (see Figure S4 in Supporting Information S1). That is consistent with previous reports on UCLs initiated from tall objects with its speed being increased with time (e.g., et al, 2014;Lu et al, 2013Lu et al, , 2015Qi et al, 2021), while it is contrary to UCLs observed on common buildings with the speed being approximately constant (e.g., Saba et al, 2017Saba et al, , 2022Saba et al, , 2023.…”

“…, 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).…”