A Positive Cloud‐to‐Ground Flash Caused by a Sequence of Bidirectional Leaders that Served to Form a Ground‐Reaching Branch of a Pre‐Existing Horizontal Channel

Abstract

High‐speed video and electric field change data were used to analyze the initiation and propagation of four predominantly vertical bidirectional leaders making connection to a predominantly horizontal channel previously formed aloft. The four bidirectional leaders sequentially developed along the same path and served to form a positive branch of the horizontal in‐cloud channel, which became a downward positive leader producing a 135‐kA positive cloud‐to‐ground (+CG) return stroke. The positive (lower) end of each bidirectional leader elongated abruptly at the time of connection of the negative (upper) end to the pre‐existing channel aloft. Thirty‐six negative streamer‐like filaments (resembling recently reported “needles”) extended sideways over ∼110 to 740 m from the pre‐existing horizontal channel at speeds of ∼0.5 to 1.9 × 107 m/s, in response to the injection of negative charge associated with the +CG.

Recoil Leader and Associated Discharge Features Observed During the Progression of a Multi‐Branched Upward Lightning Flash

“…However, due to limited temporal resolutions (90-1,000 μs) in those previous studies, the connection of a RL with a conducting channel and its subsequent discharge processes have never been properly resolved before, thus their detailed features remain unknown.Using a high-speed video camera NAC and a high-speed optical imaging system Lightning Attachment Process Observation System (LAPOS3) , we observed a special discharge progression which extended its channel not through an ordinary leader, but through a series of recoil leaders and the subsequent discharges caused by the connection of the recoil leaders to other conducting leader channels. Similar discharge progression was recently reported by Wu et al (2021). However, due to the resolution limitation (20 or 50 μs), detailed features of such a special discharge progression were not well-resolved.…”

High‐Speed Video Observations of Needles in a Positive Cloud‐to‐Ground Lightning Flash

“…As shown in Figure 1a, four predominantly vertical bidirectional leaders connected to the previously formed horizontal channel (see the junction point in Figure 1a) and lead to formation of a positive branch (see downward positive branch in Figure 1a) of the previously formed horizontal channel aloft, with this branch eventually making contact with the ground and initiating a +CG RS. Wu et al (2021) showed that the predominantly horizontal channel was also developed from a bidirectional leader channel (see their Figures 1b-1d). The inferred origination point of the bidirectional leader was located to the right of the junction point between the positive leader/RS channel and the horizontal channel.…”

“…The leader development of both the vertical and horizontal channels are examined by Wu et al (2021) in detail.…”

First Experimental Verification of Opacity for the Lightning Near‐Infrared Spectrum

“…Because the location of lightning on tall structures is relatively predictable and the probability of occurrence is relatively high, tall structures can provide a good observation platform for lightning research (Hussein et al., 2007; Ishii et al., 2014; Janischewskyj & Hussein, 1997). Since the 1930s, researchers have successfully carried out studies of lightning on tall structures, most of which are observations and analyses of electrical and magnetic characteristics and optical channel characteristics (Diendorfer & Hannes, 1980; Fan et al., 2021; Jiang et al., 2014; Kenneth et al., 2017; Lu et al., 2013; Wang, Qie et al., 2016; Warner et al., 2012; Wu et al., 2021; Yuan et al., 2017; Zhou et al., 2012). There are very few reports of spectral observations of lightning on tall structures.…”