In summer of 2019, the bandwidth of magnetic field sensor with relatively high sensitivity was extended to 1.2 MHz during the triggered lightning experiment of Field Experiment Base on Lightning Sciences, China Meteorological Administration (CMA‐FEBLS) in Conghua, Guangdong Province. The measurements with the new magnetic fields reveal the presence of microsecond‐scale magnetic pulses during the entire duration of upward positive leader (UPL), including the quiet stage when only few signals can be discerned in previous observations, which indicates that the UPL generally propagates in a stepwise manner during the initial stage of triggered lightning. Synchronous mapping observations from the broadband VHF interferometer shows that the VHF radiation corresponds to the onset of individual magnetic pulses, indicating that the VHF signals are radiated by the breakdown processes of individual stepping, and these breakdown events launch the meter‐scale current pulses as the radiation source of individual magnetic pulses.

Lightning location provides an important means for the study of lightning discharge process and thunderstorms activity. The fine positioning capability of total lightning based on low-frequency signals has been improved in many aspects, but most of them are based on post waveform processing, and the positioning speed is slow. In this study, artificial intelligence technology is introduced for the first time to lightning positioning, based on low-frequency electric-field detection array (LFEDA). A new method based on deep-learning encoding features matching is also proposed, which provides a means for fast and fine location of total lightning. Compared to other LFEDA positioning methods, the new method greatly improves the matching efficiency, up to more than 50%, thereby considerably improving the positioning speed. Moreover, the new algorithm has greater fine-positioning and anti-interference abilities, and maintains high-quality positioning under low signal-to-noise ratio conditions. The positioning efficiency for return strokes of triggered lightning was 99.17%, and the standard deviation of the positioning accuracy in the X and Y directions was approximately 70 m.

By using the synchronous observation data obtained at the Tall‐Object Lightning Observatory in Guangzhou (TOLOG) of 2019, the electromagnetic characteristics of upward positive leader (UPL) ascending from the 600‐m high Canton Tower are examined, and are compared with the magnetic field (B‐field) radiation of UPL in rocket‐triggered lightning. Before the inception of sustained UPL, small electric field (E‐field) pulses are superposed on the fast E‐field changes. The timescale of B‐field pulses corresponding to the E‐field pulses ranges from 5 to 9 μs, and the inter‐pulse interval is about 30 μs, which are both similar to the B‐field pulses associated with the precursors of rocket‐triggered lightning. Measurements show that the precursor‐like stage is likely common for upward lightning initiated from the Canton Tower. Moreover, the UPL channel of tower‐initiated upward lightning extends significantly in the first several ms with the initial average two‐dimensional (2‐D) velocity of 8.77 × 10⁵ m/s (3‐D velocity of 11.0 × 10⁵ m/s), which is one order of magnitude faster than the UPL initiated from the wire tip of rocket‐triggered lightning, indicating that initiation of UPL from Canton Tower benefits from a substantial E‐field enhancement of nearby lightning discharges. However, this favorable condition is rapidly consumed during the UPL development, causing the average 2‐D velocity of UPL to decrease rapidly and maintain at about 0.5 × 10⁵ m/s. It is noted that the variation in the 2‐D speed of sustained UPL differs from tower‐initiated upward lightning reported in the literature, which is possibly associated with the physical and geometric properties of the tower.

Precursory current pulses (precursors) and initial upward leader pulses are examined to characterize the charge transfer of precursors and the sustained upward leader during the early stage of rocket‐triggered lightning. According to the analysis of six negative triggered flashes, it is found that both precursors and the initial upward positive leader (iUPL) pulse are led by a small deflection that appears at about 25 μs prior to the major pulses. The characteristics of precursors and iUPL pulses are very similar except that the precursors generally transfer less electric charge (35.07 μC on average) than iUPL pulses do (64.73 μC on average). Some marginal differences in the parameters (e.g., rise time, duration) may be attributed to the modification of the current pulses caused by the different impedances of the leader channel and the steel wire. The ascending rocket causes the enhancement of electric field (E‐field) in the close vicinity of the wire tip, and therefore the breakdown of the iUPL is initiated by a stronger E‐field than that of the precursors. The step lengths of the precursors (defined as the extended length of the wire tip lifted by the rocket between two adjacent isolated precursors) are similar to that of iUPL pulses. Our analyses indicate that the transition from precursors to the iUPL occurs when the E‐field around the wire tip is strong enough, by the accumulation of more positive charge, to launch a meter‐scale breakdown and the ensuing charge transfer to ground.