Lightning attachment process to common buildings

Abstract

The physical mechanism of lightning attachment to grounded structures is one of the most important issues in lightning physics research, and it is the basis for the design of the lightning protection systems. Most of what is known about the attachment process comes from leader propagation models that are mostly based on laboratory observations of long electrical discharges or from observations of lightning attachment to tall structures. In this paper we use high‐speed videos to analyze the attachment process of downward lightning flashes to an ordinary residential building. For the first time, we present characteristics of the attachment process to common structures that are present in almost every city (in this case, two buildings under 60 m in São Paulo City, Brazil). Parameters like striking distance and connecting leaders speed, largely used in lightning attachment models and in lightning protection standards, are revealed in this work.

Striking Distance Determined From High‐Speed Videos and Measured Currents in Negative Cloud‐to‐Ground Lightning

“…The most accurate approach to estimate the SD is considered the reverse propagation procedure adopted in this work (four events). The differences between the propagation speeds of the positive and negative leaders calculated in this work and in Saba et al () suggest that assuming a same speed for both leaders, as done by Tran and Rakov () and Wang et al (, ) leads to underestimation of the SD. On the other hand, adopting a general composite propagation speed in the last 300 m propagated distance, as used in this work for estimating the SD of 17 first return strokes from records of current, is expected to yield moderate errors, as demonstrated by the SD calculated for events A, B, and C, which exhibit a maximum error of 18%.…”

“…Based on high‐speed videos, Tran and Rakov () estimated SD of 14 first return strokes and new ground terminations. In high‐speed videos, Saba et al () detected the initiation of the upward leader from a 50 m high building and estimated the striking distance of three subsequent RSs. Using LAPOS, Wang et al () reported the initiation height of four RSs, including two first RSs.…”

High‐Speed Video Observations of Natural Lightning Attachment Process With Framing Rates up to Half a Million Frames per Second

“…Mazur et al () assumed the ratio to be equal to 2. Dellera and Garbagnati (, ) assumed this ratio to change from 4 to 1 during the attachment process, and Saba et al () showed that the ratio was from 2.3 to 4.8. In this study, we found that the average speed of SDL‐1 was 0.9 that of UCL (very close to their connection).…”

“…The speed of upward positive leader at its initiation is studied by high-speed video camera in recent years (e.g., Biagi et al, 2011;Jiang et al, 2014;Saba et al, 2017). Saba et al (2017) using high-speed video cameras observed three attachment processes occurred on two buildings under 60 m. Three UCLs from lightning rods move at a constant speed, ranging between 4.3 and 6.2 × 10 4 m/s. Visacro et al (2017) discussed different approaches to estimating the SD from high-speed video and current records.…”

“…• Figure S2 • Figure S3 • Movie S1 Warner, 2010), on common multi-storey buildings (Saba et al, 2017), and on ground or on trees (e.g., Jiang et al, 2015;Tran & Rakov, 2015. Most of the observations have been made for lightning terminating on high-rise buildings or isolated towers in cities.…”