We introduce the empirical mode decomposition algorithm and applied low‐frequency filtering and high‐frequency noise reduction to the waveform of the electric field changes recorded in 1‐ms segments. This algorithm greatly improved the accuracy of the peak time extraction and the number of pulses in the low and very low frequency band, which enhanced the accuracy in positioning the pulse of the electric field change. Compared with the previous algorithm, the algorithm can significantly reduce the time error, giving a better positioning result. With a time error estimate of 100 ns and a limit of goodness of fit less than 5, the number of pulse locations is increased by nearly 7 times. The goodness‐of‐fit distribution of the pulse location results had a normal distribution, and the 95% confidence interval of goodness of fit was 0–4; the corresponding positioning space error was <60 m. The continuity of the lightning channel was significantly improved, and the development characteristics and fine structure of the lightning channel were clearly distinguished. The low‐frequency electric field detection array system gave detailed positioning results for a bolt from the blue lightning strike. By comparing the results from the low‐frequency electric field detection array with the actual lightning strike point, we objectively demonstrated the positioning performance of the new algorithm. The system gave positioning results for the lightning for all seven return strokes. The maximum horizontal distance between the locating point and the real lightning strike point was 57 m, the minimum horizontal distance between them was 3 m, and the mean distance was 27 m.

The production mechanism for terrestrial gamma ray flashes (TGFs) is not entirely understood, and details of the corresponding lightning activity and thunderstorm charge structure have yet to be fully characterized. Here we examine sub-microsecond VHF (14-88 MHz) radio interferometer observations of a 247-kA peak-current EIP, or energetic in-cloud pulse, a reliable radio signature of a subset of TGFs. The EIP consisted of three high-amplitude sferic pulses lasting ≃60 μs in total, which peaked during the second (main) pulse. The EIP occurred during a normal-polarity intracloud lightning flash that was highly unusual, in that the initial upward negative leader was particularly fast propagating and discharged a highly concentrated region of upper-positive storm charge. The flash was initiated by a high-power (46 kW) narrow bipolar event (NBE), and the EIP occurred about 3 ms later after ≃3 km upward flash development. The EIP was preceded ≃200 μs by a fast 6 × 10 6 m/s upward negative breakdown and immediately preceded and accompanied by repeated sequences of fast (10 7-10 8 m/s) downward then upward streamer events each lasting 10 to 20 μs, which repeatedly discharged a large volume of positive charge. Although the repeated streamer sequences appeared to be a characteristic feature of the EIP and were presumably involved in initiating it, the EIP sferic evolved independently of VHF-producing activity, supporting the idea that the sferic was produced by relativistic discharge currents. Moreover, the relativistic currents during the main sferic pulse initiated a strong NBE-like event comparable in VHF power (115 kW) to the highest-power NBEs.

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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. Plain Language Summary The magnetic field sensor with high sensitivity has demonstrated its capability to resolve the weak discharging processes during the initial upward leader of rocket-triggered lightning. However, the bandwidth of the magnetic sensor used in previous measurements was usually below 500 kHz, which restricts the identification of more impulsive discharging processes with microsecond time scale. In order to improve the understanding on the development of initial upward leader in triggered lightning, new measurements were conducted by extending the upper bandwidth of magnetic sensor to 1.2 MHz and comparing with the very high-frequency (VHF) interferometric mapping observations. Benefitting from the extension of bandwidth to higher frequency, the microsecond-scale magnetic pulses associated with the upward positive leader are unambiguously resolved during the "quiet" stage for the first time, when few signals could be discerned in previous measurements. Many of these pulses cannot be resolved in the measurement of channel-base current and fast/slow electric fields. Consequently, the measurements with the improved sensor help to reveal more features for the development of upward leader during the initial stage of triggered lightning. By comparing with the synchronous VHF signals, it is found that the VHF radiation and mid-/low-frequency magnetic field manifest different discharging processes of the upward leader.

Based on fast electric field waveforms of the Low‐frequency E‐field Detection Array (LFEDA), we introduce the time reversal technique into lightning three‐dimensional location for the first time and propose a new algorithm for the three‐dimensional location of lightning low‐frequency discharges. Without using complex filtering algorithms to remove higher‐frequency component, this method obtains similar results to the newly reported LFEDA refinement algorithm. The new algorithm can obtain finer, more continuous, and richer positioning results with a minimum of four stations, 5‐dB signal‐to‐noise ratio, and 500‐ns time error compared with the low‐frequency signal time of arrival three‐dimensional positioning method. These results indicate that the new algorithm has the advantages of low requirements on the number of stations, certain anti‐interference ability, and low requirements on time accuracy. The standard deviations in the X and Y directions for return strokes of triggered lightning flashes are both approximately 90 m.