The evolution of charge structure involved in lightning discharge of a thunderstorm over the central Tibetan Plateau is investigated for the first time, based on the data from very high frequency interferometer, radar and sounding. During the developing‐mature stage, the TP thunderstorm exhibited a tripolar charge structure evolved from an initial inverted dipole. At the mature stage, a bottom‐heavy tripole charge structure is clearly presented, with a strong lower positive charge center (LPCC) at temperatures above −10°C, a middle negative charge region between −30°C and −15°C, and an upper positive charge region at T < −30°C. As the LPCC was depleted, the charge structure evolved into a normal tripole with a pocket LPCC. The merging between different convective cells resulted in the formation of two adjacent negative charge regions located directly and obliquely above the LPCC, and horizontally arranged different charge regions were simultaneously involved in the same lightning discharge.

A rocket‐triggered lightning flash containing negative‐positive‐negative current polarity reversal during its initial stage is analyzed using multiple synchronized observation data. The flash was triggered under a thunderstorm transition zone between the convective region and the stratiform region. The upward positive leader branched and developed toward the stratiform region. When the negative initial continuous current was decreasing, a negative stepped leader was transformed from a recoil leader on a preexisting positive branch. As the negative leader developed toward the convective region, a breakdown process initiated on a preexisting positive channel and propagated toward the back end of the negative stepped leader, accompanied with a positive electric field change pulse. The current polarity changed from negative to positive about 0.22 ms after the onset of the breakdown process. The negative leader terminated after propagating for 71.08 ms, while scattered discharges on other positive branches maintained to develop, and then the ICC polarity changed from positive to negative.

Lightning very high frequency interferometry is a crucial tool for studying the development of lightning leaders within thunderclouds, and the conventional antenna array is composed of two coplanar orthogonal baselines. In this study, we develop two new location methods for an irregular array based on the optimization algorithm, using all baselines in the calculation. Besides, we have analyzed the effects of two kinds of time uncertainty on the location result and provided a calibration method. The first type—the systematic time drift of antennas—can induce an offset on the location result, leading to a worse accuracy. We can calibrate the time drift of each antenna efficiently during the experiment. The second type—the waveform distortion between different antennas—can introduce the noise on time, leading to worse precision. The location precision improves when more baselines are used, whether they are independent or redundant. Our result shows that the non‐coplanar configuration can significantly improve the elevation uncertainty near the horizon and the azimuth uncertainty near the zenith after considering the angular uncertainty's theoretical distribution.

Very-high-frequency (VHF) electromagnetic signals have been well used to image lightning channels with high temporal and spatial resolution due to their capability to penetrate clouds. A lightning broadband VHF interferometer with three VHF antennas configured in a scalene-triangle shape has been installed in Lhasa since 2019, to detect the lightning VHF signals. Using the signals from the VHF interferometer, a new hybrid algorithm, called the TDOA-EMTR technique, combining the time difference of arrival (TDOA) and the electromagnetic time reversal (EMTR) technique is introduced to image the two-dimensional lightning channels. The TDOA technique is firstly applied to calculate the initial solutions for the whole lightning flash. According to the results by the TDOA method, the domain used for the EMTR technique is predetermined, and then the EMTR technique is operated to obtain the final positioning result. Unlike the original EMTR technique, the low-power frequency points for each time window are removed based on the FFT spectrum. Metrics used to filter noise events are adjusted. Detailed imaging results of a negative cloud-to-ground (CG) lightning flash and an intra-cloud (IC) lightning flash by the TDOA method and the TDOA-EMTR are presented. Compared with the original EMTR method, the positioning efficiency can be improved by more than a factor of 3 to 4, depending on the scope of the pre-determined domain. Results show that the new algorithm can obtain much weaker radiation sources and simultaneously occurring sources, compared with the TDOA method.

Negative‐polarity lateral discharges on pre‐ionized negative channels during a positive cloud‐to‐ground lightning flash were captured by very high frequency interferometric observations. Prior to the return stroke (RS), as the positive leader (PL) advanced steadily and the negative leader (NL) weakened, flickering lateral re‐discharges with small scale, resembling needles on PLs, propagated toward the NL tip at approximately 8.0 × 10 ⁴ m/s. Unlike needles concentrated near PL tips, these re‐discharges occurred along nearly the entire horizontal negative channel. Following the RS, both fast discharges along existing negative channels and new lateral discharges breaking into virgin air were observed, rapidly extending the negative channels and sustaining the continuing current. These re‐discharges appeared to be closely linked to channel potential variations: gradual potential changes before the RS reactivation preceded negative branches, while abrupt potential jumps after the RS initiation triggered intense axial and lateral discharges.

A rocket-triggered lightning flash containing negative–positive–negative current polarity reversal during its initial stage is analyzed using multiple synchronized observation data. The flash was triggered under a thunderstorm transition zone between the convective region and the stratiform region. Both positive leaders developing in the transition zone and negative leaders developing toward the convective region could be identified. As the negative initial continuous current (ICC) declined, a negative leader was transformed from a recoil leader which turned to break down virgin air off the preconditioned positive leader branch. As the negative leader developing forward, a reactivated breakdown leader bridging the grounding trunk channel and the initiation region of the negative leader caused the current polarity reversed from negative to positive 0.22 ms later, which is reported for the first time. The negative leader channel terminated after propagating for 71.08 ms, and the ICC reversed to be negative again owing to the propagation of another positive branch. The horizontal dipole charge structure contributed to the branching of positive leader and the initiation of negative leader, which combined to produce the upward bipolar lightning. During the positive ICC stage, both positive and negative channels simultaneously contributed to the channel-base current and several negative recoil leaders injecting negative charge to the grounding trunk channel produced a fast decrease of the current.