Using high‐speed video cameras operating with framing rates of 20 and 525 kfps, we imaged the attachment process of a natural negative cloud‐to‐ground flash, occurring at a distance of 490 m. Nine upward leaders were observed. A total of 12 space stems/leaders in 47 steps of the downward negative stepped leader were captured. The two‐dimensional length of them was between 2.0 and 5.9 m, with an average of 3.0 m. The average interstep interval, step length, and two‐dimensional speed of the downward negative leader and that of upward positive leader were statistically analyzed. The last step of the downward negative leader making contact with the upward connecting leader was recorded. The two‐dimensional length of the final imaged gap between the tips of opposite‐polarity leaders was estimated to be about 13 m.

A positive cloud‐to‐ground (+CG) lightning flash containing a single stroke with a peak current of approximately +310 kA followed by a long continuing current triggered seven upward lightning flashes from tall structures. The flashes were observed on 4 June 2016 at the Tall Object Lightning Observatory in Guangzhou, Guangdong Province, China. The optical and electric field characteristics of these flashes were analyzed using synchronized two‐station data from two high‐speed video cameras, one total‐sky lightning channel imager, two lightning channel imagers, and two sets of slow and fast electric field measuring systems. Three upward flashes were initiated sequentially in the field of view of high‐speed video cameras. One of them was initiated approximately 0.35 ms after the return stroke of +CG flash from the Canton Tower, the tallest structure within a 12‐km radius of the +CG flash, while the other two upward flashes were initiated from two other, more distant tall objects, approximately 18 ms after the +CG flash stroke. The initiation of the latter two upward flashes could be caused by the combined effect of the return stroke of +CG flash, its associated continuing current, and K process in the cloud. Each of these three upward flashes contained multiple downward leader/upward return stroke sequences, with the first leader/return stroke sequence of the second and third flashes occurring only after the completion of the last leader/return stroke sequence of the preceding flash. The total number of strokes in the three upward flashes was 13, and they occurred over approximately 1.5 s.

High‐speed video data were used to analyze the initiation and propagation of 36 needles and their associated 306 flickering events observed in a single‐stroke positive cloud‐to‐ground (+CG) flash. The needles occurred during the return‐stroke later stage and the continuing current, within approximate 10 ms after the onset of the +CG return stroke. They initiated near the lateral surface of the predominantly horizontal channel and extended almost perpendicular to that channel. Flickering events are recoil type streamers (or leaders) that retrace the channels created by needles. Flickering events can be repetitive and are classified into four categories based on different scenarios of their occurrence. Needles are caused by the radial motion of negative charge from the hot core of the positive‐leader channel into the positive corona sheath surrounding the core, when the core is rapidly recharged (its radial electric field reversed) by the return‐stroke process and during the following continuing current.

High‐speed video and electric field change data have been used to examine the initiation and propagation of 21 recoil leaders, 7 of which evolved into dart (or dart‐stepped) leaders (DLs) initiating return strokes and 14 were attempted leaders (ALs), in a Canton‐Tower upward flash. Three DLs and two ALs clearly exhibited bidirectional extension. Each DL was preceded by one or more ALs and initiated near the extremity of the positive end of the preceding AL. The positive end of each bidirectional DL generally appeared to be inactive (stationary) or intermittently propagated along the positive part of the preceding AL channel and extended into the virgin air. A sequence of two floating channel segments was formed ahead of the approaching positive end of one DL, causing its abrupt elongation.

It has been determined that the discharge of lightning current to ground through grounding grid results in high potential at the grounding grid and other nearby grounding grids, which is very destructive. In the present paper, based on artificial lightning trigger technology, the characteristics of the ground potential rise (GPR), the transient effect at the active grid under the transient impulse of lightning current was analyzed. The impulse ground resistance is found to decrease for large input currents, On the other hand, for small input currents it usually increases. In addition, the characteristics of the transfer potential of the passive grid which is located 40 m from the active grid were analyzed, and it was shown that the peak value of the transfer potential at the passive grid was approximately 5.1% of the peak value of the ground potential at the active grid during the return stroke. The achievements made in this study may contribute toward the optimization of the simulation model.