An uncommon three‐stroke positive cloud‐to‐ground (+CG) lightning flash was observed by synchronous multifrequency radiation sensors, and the three‐dimensional development of the channel was carefully mapped. Results show that three positive strokes grounded at different points approximately 4–8 km apart and time intervals between neighboring +CG strokes were 85 and 222 ms, respectively. This +CG flash was preceded by an intracloud (IC) discharge. The locations of the termination points on the ground were just below the preestablished horizontal IC discharge channels, and the three strokes were linked with each other through sharing horizontal negative leader channels inside the cloud. There were stepping pulses less than 0.4 ms before the first and second return strokes (RSs), and their location results were distributed nearby the following RS, indicating that the pulses might be associated with the attachment process. The first and second positive strokes occurred when the horizontal in‐cloud negative channel stopped extending, while the third positive stroke occurred below the opposite end of an advancing negative leader in the cloud. The above results suggest that the downward positive leader preceding the strokes possibly developed either from different decayed leader channels or from the opposite end of an advancing leader channel. A high‐speed camera captured a downward positive attempted leader from another +CG flash, revealing how a downward positive leader incepted from a horizontal negative lightning channel.

Fine time‐resolved images of the development of lightning bidirectional leaders below the cloud base were captured by a high‐speed camera in association with multiband electromagnetic field measurements. The bileaders tended to originate at a radial distance of about 200 m from a progressing positive leader channel, propagating more or less radially toward and away from the main channel. Significant asymmetrical channel extensions at opposite ends were clearly recognized. The positive ends of the bileaders propagated in single paths with average speed of 6.1 × 10⁴ m/s, while the opposite negative end involved obvious branching and stepping propagation with average speed of 1.6 × 10⁵ m/s. The bidirectional leaders eventually connected to the existing main positive leader, producing new branches of the flash. Another cause of positive leader branching was that the positive leader split at its head and developed into different branches synchronously, which were sometimes invisible but were revealed by recoil leaders.

We identify and investigate the intermittent propagation of upward positive and negative leaders in rocket‐triggered lightning based on comprehensive observations of fine time‐resolved optical, current, and electromagnetic fields. There is an abrupt luminous crown blooming due to the achievement of a positive leader step, after which the channel weakens and the head degrades. During the positive leader pausing, residual structure is recognized at area of previous luminous crown blooming, in the form of a floating segment. Our observation point to a possible mechanism that it connects with the positive leader head, causing a forward‐step and a sharp current pulse. This is to some extent similar to negative leader stepping, in which the space leader emerges and connection between the space leader and the channel head occurs. The generation of clustered space leaders give rise to negative channel branching, but the residual structure in positive leader just leads to individual step.

Both upward positive connecting leader (UPL) and downward negative leader (DNL) involved in a lightning striking the 325‐m meteorology tower were captured by using a high‐speed video camera with 2.7‐μs temporal resolution and 1‐m spacial resolution, in association with electromagnetic field measurements. The UPL initiated around 1.6 ms prior to the attachment when the DNL was outside the field of view of the camera, and 38 hop forwards with backward re‐illumination through the UPL channel were identified. As the stepped DNL approached, 34 space stems were observed in front of the leader tip during 0.62‐ms period prior to the attachment, while, based on the present observation system, no visible space stem was found throughout the intermittent UPL propagation. The 2‐D propagation speed of the UPL and DNL was 1.16 × 10⁵ and 3.6 × 10⁵ m/s, within channel extensions of 100 and 95 m, respectively. For the UPL, the inter‐step interval was longer in its initial development while the step length was similar throughout the propagation. Several steps of DNL could be identified within an inter‐step of UPL, and vice versa. The different intermittent behaviors of negative and positive leaders with temporal‐inconsistent steps suggest that their stepping was independent from each other. When the DNL was very close to the UPL, the DNL can induce and support the UPL development by enhancing the overall electric field. However, it seems that the generation of space stems and their bridging to the DNL, as involved in the DNL stepping, might not the direct cause of the UPL intermittence.

A lightning flash striking a 325‐m tower was captured using a high‐speed camera operated at 380 kfps and the characteristics of breakthrough phase (BTP) were recorded in two consecutive frames. The fine time‐resolved images indicate that the common streamer zone (CSZ) formed when the bright tips of negative and positive leaders were ≥23 m apart from each other. During BTP, both the negative and positive leaders extended their channels with enhanced luminosity and the gap between them was shortened to 16 m in the frame prior to return stroke. A space leader‐like luminous segment was found within the route of leader connection. This route is inferred to have already been determined at the initial formation of CSZ, by the interconnected streamers of approaching leaders. The dominant growth of this route is interpreted as a new scenario for the conversion of a high‐impedance CSZ to a hot plasma channel during BTP.