Yang Zhang

The shape of lightning channels reflects nature's intricate craftsmanship, shaped by intracloud electric fields influenced by the microphysical structure of thunderstorms. While previous studies have focused primarily on the relationship between vertically stratified charge structures and vertical lightning development, the relationship between thunderstorm microphysics and the horizontal development of lightning remains unclear. This study uses three‐dimensional radiation source data from the Lightning Mapping Array at New Mexico's Langmuir Laboratory and KABX radar data to examine how the types, number concentrations, and spatial arrangement of hydrometeors influence the horizontal development of lightning within a certain range of altitudes. The WRF‐Electric model is employed to validate the observations. The results show that horizontal microphysical heterogeneity alters the evolution characteristics of lightning channels: branching and acceleration often occur at boundaries between different types of hydrometeors, in regions with high particle number concentrations, and near regions of vertical ice. Simulations further reveal that turbulence strongly influences the distribution of hydrometeors and that the type of hydrometeor has a greater effect on the electric field variation than does the number concentration. This study establishes a clear correspondence between thunderstorm microphysics and the horizontal development of lightning, and clarifies how microphysical structure affects lightning development.

Employing the multi‐station Thunderstorm Energetic Radiation Observation System, we detected X‐ray bursts during two rocket‐triggered lightning events in 2024. By innovatively integrating optical imaging with three‐dimensional lightning channel reconstruction based on Distributed Acoustic Sensing (DAS), we analyzed the X‐ray emission characteristics from these events. During the Tl_20240812 event, lateral deflection of a descending negative leader resulted in X‐rays being detected exclusively by a distal sensor. This clear spatial correlation provides direct and conclusive geometric evidence that the radiation is emitted in a beam‐like pattern along the leader propagation path. Furthermore, based on the Tl_20240801 event, this study achieved the first quantitative estimation of the X‐ray photon beam half‐angle width, determined to be between 40° and 46°. This angular range aligns with the predicted structure of the leader tip electric field, thereby providing robust support for the hypothesis that X‐rays originate from the leader tip high‐field runaway electron mechanism.

Eleven unusual precursors were observed in the initial stage of a classical triggered lightning event, which was performed on CMA‐FEBLS in the summer of 2024. The amplitudes of these unusual leaders exceeded 300 A, with pulse intervals from 30 to 200 ms, while their initiation height was only about 30 m. Once these attempted leaders surpassed 250 m, they resumed the development pattern of conventional precursors. The analysis suggested that the occurrence of unusual precursors is related to the existence of the space charge layer, as the event occurred under thunderstorm conditions with sparse natural discharges, which facilitated its accumulation. When subjected to airflow or precipitation, the space charges were susceptible to localized abrupt diminution or dissipation. Such changes induced anomalous enhancements in the electric field intensity at the wire's tip as it traversed through the space charge region, ultimately leading to the occurrence of unusual precursors.

On 18 July 2023, X‐ray emissions associated with two rocket‐triggered lightning flashes were observed at the Field Experiment Base for Lightning Sciences, China Meteorological Administration. In this paper, the relationship between X‐ray characteristics and propagation speed of downward negative dart leaders is analyzed for the first time. Results show that within the same lightning flash, there is a strong positive correlation between the leader brightness and its 2D speed, as evidenced by a high correlation coefficient, R, of +0.94. Consistently, the intensity of X‐rays generally exhibits a positive correlation with the leader 2D speed. Conversely, the average X‐ray pulse interval is negatively correlated with the leader 2D speed, with a significant correlation coefficient, R, of −0.93. Furthermore, the intervals of partial steps of dart leader can be characterized by the intervals between the X‐ray pulses.

Most real‐time lightning location systems are based on feature matching to locate lightning, but they often lack the ability to locate lightning channels. To achieve lightning channel location based on feature matching, a new location algorithm is proposed by utilizing time series segmented feature to match lightning pulses. The features of waveform time series do not require complex signal processing, making it suitable for real‐time and fast location. Compared with the location results of the other three existing methods for a lightning event, the new method achieves the highest matching efficiency of 28.4% and demonstrates fine channel location capability. For a thunderstorm process, the new method also has the highest location efficiency, as well as the highest number of valid location points per second, and the lowest computation time of per valid location point, which are 26%, 39.6, and 0.025s, respectively. The new algorithm also provides better location results for irregular pulse clusters, which more realistically depict the development process of downward leader compared to the location methods based on encoding feature matching. This may be caused by the fact that the time series segmented feature can correctly represent the change trend of the signal under the condition of low signal‐to‐noise ratio.

Altitude‐triggered lightning provides favorable conditions for the research of bidirectional leader system. In the summer of 2023, altitude‐triggered lightning experiment was conducted on the Field Experiment Base on Lightning Sciences, China Meteorological Administration. The multifrequency radiation characteristics of bidirectional leaders and the interactions of both ends during the propagation are analyzed. Specifically, the discharge processes that produce LF‐MF magnetic radiations from bidirectional leaders are revealed by high‐speed images, and these LF‐MF radiations correspond to the VHF radiations generated by bidirectional leaders well. Unlike the strong correlation between LF‐MF radiation strengths and discharge intensities, the VHF radiation strengths exhibit significant variation even among similar‐intensity discharge events, as VHF radiations correspond to the random and microscopic discharge processes associated with streamers. Furthermore, the changes in leader speed and channel brightness before and after the initiation of bidirectional leaders indicate that the development of the two ends of bidirectional leaders is mutually reinforcing.

Observations of a regular pulse burst (RPB) at the end of a K‐event are analyzed utilizing a simple geometric model and particle swarm optimization (PSO) to estimate the currents and propagation speeds of successive pulses of the RPB. The results show that the current of successive pulses is strongly overlapped and, for typical speeds of continuously propagating K‐events, are unphysically large (88 kA), exceeding the currents of most strokes to ground. By default, the unphysical nature of the result, coupled with very high frequency interferometer observations of an RPB in Florida, shows that the propagation speed of the pulses is significantly faster than expected, namely ∼0.6–1.8 × 10⁸ m/s. This reduces the inferred current from 88 kA down to 6–18 kA, typical of intracloud events. The fast propagation speed of the stepping is explained by successive pulses retracing much of the path of the preceding pulses due to the successive pulses being strongly overlapped.

At present, for business lightning positioning systems, the classification of lightning discharge types is mostly based on lightning pulse signal features, and there is still a lot of room for improvement. We propose a lightning discharge classification method based on convolutional encoding features. This method utilizes convolutional neural networks to extract encoding features, and uses random forests to classify the extracted encoding features, achieving high accuracy discrimination for various lightning discharge events. Compared with traditional multi-parameter-based methods, the new method proposed in this paper has the ability to identify multiple lightning discharge events and does not require precise detailed feature engineering to extract individual pulse parameters. The accuracy of this method for identifying lightning discharge types in intra-cloud flash (IC), cloud-to-ground flash (CG), and narrow bipolar events (NBEs) is 97%, which is higher than that of multi-parameter methods. Moreover, our method can complete the classification task of lightning signals at a faster speed. Under the same conditions, the new method only requires 28.2 µs to identify one pulse, while deep learning-based methods require 300 µs. This method has faster recognition speed and higher accuracy in identifying multiple discharge types, which can better meet the needs of real-time business positioning.

Lightning channel morphology depends on the thunderstorm cloud charge structure, which in turn is influenced by the thunderstorm dynamics. In this paper, based on three‐dimensional radiation source localization data from the Lightning Mapping Array and radar‐based data, our analysis shows that the overall morphology and detailed morphology of the lightning channel correspond to different eddy dissipation rate (EDR) characteristics. Lightning with complex channel morphology occurs in regions with large EDRs. In single lightning events, channels that extend directly within a certain height range without significant bifurcation and turning tend to propagate in the direction of decreasing EDRs, while channel bifurcations and turns usually occur in regions with large radial velocity gradients and large EDRs. This study shows the relationship between channel morphology and thunderstorm dynamics and provides a new method for the direct application of channel‐level localization data to understand thunderstorm dynamics characteristics.

At present, there is still some uncertainty in the evaluation of the performance of the Fengyun 4A Lightning Mapping Imager (LMI), which is mainly limited by the detection performance of the reference detection system and the suitability of the evaluation method. In this paper, a one-to-one performance evaluation of the LMI was performed based on total lightning flash data from the lightning Low-Frequency Electric field Detection Array (LFEDA). It was found that there were significant systematic biases in the discharge results detected via LMI, with a median of −0.946 s, −0.0817°, and −0.0245° in time bias, longitude bias, and latitude bias, respectively. The evaluation results after removing the systematic biases indicated that the relative detection efficiency for flashes of LMI was 17.6%, the mean and median time errors were both 0.647 s, and the mean and median distance errors were 6.09 km and 5.02 km, respectively. The relative detection efficiency for groups of LMI was 9.8%, the mean and median time errors were 0.674 s and 0.660 s, and the mean and median distance errors were 7.19 km and 6.54 km, respectively. The detection efficiency of LMI for both flashes and groups at nighttime was significantly higher than its detection efficiency during the daytime. The relative detection efficiency for flashes of LMI at nighttime was 26.5%, while during the daytime it was 14.4%. The relative detection efficiency for groups of LMI at nighttime was 16.2%, while during the daytime it was only 7.4%. The spatial accuracy for both flashes and groups was always better during the daytime than at nighttime.