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The current methods for lightning risk warnings that are based on atmospheric electric field (AEF) data have a tendency to rely on single features, which results in low robustness and efficiency. Additionally, there is a lack of research on canceling warning signals, contributing to the high false alarm rate (FAR) of these methods. To overcome these limitations, this study proposes a lightning risk warning method that incorporates enhanced empirical Wavelet transform-Adaptive Savitzky–Golay filter (EEWT-ASG) and one-dimensional morphology, using time-frequency domain features obtained through the Wavelet transform (WT). The proposed method achieved a probability of detection (POD) of 77.11%, miss alarm rate (MAR) of 22.89%, FAR of 40.19%, and critical success index (CSI) of 0.51, as evaluated on 83 lightning events. This method can issue a warning signal up to 22 min in advance for lightning processes.

The current methods for lightning risk warnings that are based on atmospheric electric field (AEF) data have a tendency to rely on single features, which results in low robustness and efficiency. Additionally, there is a lack of research on cancelling warning signals, contributing to the high false alarm rate (FAR) of these methods. To overcome these limitations, this study proposes a lightning risk warning method that incorporates enhanced empirical Wavelet transform-Adaptive Savitzky Gorey filter (EEWT-ASG) and one-dimensional morphology, using time-frequency domain features obtained through the Wavelet transform (WT). The proposed method achieved a probability of detection (POD) of 77.11%, miss alarm rate (MAR) of 22.89%, FAR of 40.19%, and critical success index (CSI) of 0.51, as evaluated on 83 lightning processes. This method can issue a warning signal up to 22 minutes in advance for lightning processes.

Currently, the number of lightning casualties and casualty rates have significantly reduced in developed countries, but there has been no significant reduction in developing countries. On the one hand, this is due to the high frequency of lightning; on the other hand, the vulnerability of people in developing countries is also an influencing factor. Through case analysis and summary, this paper expounds on lightning injury’s mechanism and clinical manifestations. It points out that lightning injury is mainly related to heart problems and the impact on the nervous system, rather than burns, which usually cause fewer consequences. Medical treatment needs to pay attention to the order and principles of treatment. Implementing CPR and auxiliary AED is the most effective way to save lives. Attention should be paid to the practical and effective treatment and nursing of lightning stroke sequelae. Finally, combined with the situation of lightning casualties in china, the existing problems are put forward during the process of early treatment, post-hospital treatment, and nursing observation, which provides an objective basis for the cognition of the scientific nature of the lightning injury.

The effects of real terrain on the lightning magnetic fields and location accuracy are studied by using two-dimensional finite difference time-domain method. Two estimation methods of wave arrival time (using the time corresponding to the peak field and 10% threshold of the peak field) are applied to the arrival time delay, and then using the ToA technique with three approaches of arrival time differences to evaluate the location accuracy. It is found that the effect of real terrain on the lightning magnetic fields is due to the enhancement of reflection wave and propagation attenuation of terrain topography. The arrival time of peak value method is delayed from 0.15 to 2.3 μ s, while that of 10% threshold method varied from −0.11 to 0.92 μ s. The lightning location accuracy using the 10% threshold method is least, about tens of meters. Furthermore, considering the specific frequency bandwidth of detection sensors, three-order 10- to 500 kHz Butterworth filter was applied. After filtering, the effect of real terrain on the lightning magnetic fields becomes more obvious. The 10% threshold method is still the best way for lightning location, and the frequency bandwidth of different sensors on the effect of the location accuracy cannot be ignored.

Mueller matrix polarization imaging is a new biomedical optical imaging method that can generate both polarization and isotropic intensity images of structures of the biological tissue sample surface. In this paper, a Mueller polarization imaging system in the reflection mode is described for obtaining the Mueller matrix of the specimens. Diattenuation, phase retardation, and depolarization of the specimens are derived by using the conventional Mueller matrix polarization decomposition method and a newly proposed direct method. The results show that the direct method is more convenient and faster than the conventional decomposition method. The polarization parameter combination method is then presented in which any two of the diattenuation, phase retardation, and depolarization parameters are combined, and three new quantitative parameters are defined in order to reveal more detailed anisotropic structures. The images of in vitro samples are presented to demonstrate the capability of the parameters introduced.

Observational data from the low-frequency electric-field detection array (LFEDA) and radar were used to study the precise location of a fatal accident caused by a lightning in Conghua, Guangzhou, China, 2017. Based on a comprehensive analysis, the lightning was concluded to be a negative “bolt from the blue” ground flash with seven return strokes. The first return stroke was on June 3 at 16:36:49.219 with a peak current intensity of −30.9 kA. The LFEDA system mapped the development of the lightning channel. The horizontal distance from the edge of the cloud anvil area (0 dBz) to the return stroke point was about 0.3 km, the horizontal distance from the edge of the precipitation area (18 dBz) to the return stroke point was about 1.8 km, and the return stroke channel extended as far as 3 km out of the cloud. There was no cloud cover above the head of the victim. The electric field waveform of the return strokes detected by the LFEDA system showed multi-peak characteristics, and all seven return strokes were multiple-termination strokes. The most probable mechanism for the lightning injuries was the side flash.

The millimeter wave cloud radar (MMCR) is capable to detect microparticle features in the cloud and to describe the microphysical structure. Clear-air echo is a major type of false echoes (caused by non-meteorological factors) of MMCR. Therefore, analysis of clear-air echoes is valuable for cloud observation. This work analyzes the physical characteristics of the clear-air echoes, and discusses the possible features which could be extracted from products of four devices: MMCR, laser-ceilometer, L-band radiosonde and all-sky camera. The simulation results show that all the extracted features have different probability distributions for clear-air echoes and meteorological echoes. Therefore, the conclusion of this paper has potential application for identifying clear-air echoes from meteorological echoes.

Investigation and analysis of a lethal event caused by a lightning discharge in Conghua, Guangzhou, in 2017, is presented in this paper. The lightning strike first hit a tree with a height of 13m, and then hit the head of a person near the tree, causing death. The data from the Low Frequency Electric Field Detection Array, Guangdong Lightning Location System, and a nearby radar station, were analyzed. The event was identified as a lightning death incident caused by “a bolt from the blue”. The accident discharge was found to be the first return stroke (RS) with a current peak of -30.9kA, which belonged to a cloud-toground lightning flash with seven RSs. The flash initiated at a height of about 13km. At a height of 2.8km, the horizontal distance from the lightning disaster point to the edge of precipitation (18dBZ) was about 3.6km, and to the edge of the convective core (30dBZ) was about 6km. At a height of 7km, the horizontal distance of the initiation point to the edge of precipitation (18dBZ) was about 0.3km, with the distance to the edge of the convective core (30dBZ) being about 3.5km. According to the equivalent circuit model of the lightning strike, we calculated the air breakdown voltage of the side flash and step voltage on the ground. The results indicated that the event process involved the flash hitting the tree, the current flowing to the “jump point”, and then the side stroke to the victim. Crucially, the victim was exposed by a step voltage of 78.3kV, while a witness, who was 10 m from the lightning strike point, was only exposed to 0.783kV.

[1] High-speed video camera records, with a temporal resolution of 20 µs and a spatial resolution of 2.4 m per pixel, of a downward negative lightning flash that terminated on a 440 m high building are examined. The attachment process in this flash exhibited an unexpected behavior in that the downward leader tip connected to the lateral surface of the ~400 m upward connecting leader (UCL) below its tip. It appears that the effect of the downward leader on the UCL is significant, while the effect of the UCL on the downward leader is negligible, except for the final 80 µs preceding the beginning of the first return stroke. The ratio of speeds of the downward leader and the UCL tends to decrease with time, ranging from 1.8 to 0.12, although the lower 80–100 m or so of the UCL were too faint to allow speed measurements.

[1] Forty-five unconnected upward leaders (UULs) occurred in 19 downward negative flashes are analyzed. Each observed UUL is initiated by a downward stepped leader before a new strike point is struck. For each UUL, several parameters are determined when possible mainly by using high-speed images: inception height, inception time prior to return stroke (RS), horizontal distance from the flash's strike point, two-dimensional (2D) distance between the nearest downward leader branch tip and the UUL's inception point at its inception time, 2D length, and 2D average propagation velocity. Their values range from 40 to 503 m (number of samples: 45)

More than ten unconnected upward positive leaders initiated from high structures in response to natural downward-moving negative leaders are analyzed. These leaders are observed by using high-speed cameras with sampling rates at the order of 104 fps (frames per second). The propagation velocity, channel width of the unconnected upward leader and the distances between it and strike point are presented. The results can deepen our understanding of the lightning attachment process.

The artificially triggered lightning test was conducted and a 4-element AWS (Automatic Weather Station) was simulated near the lightning channel. This paper analyzes and studies the induced effects caused by the near lightning on the signal line and the key lightning protection techniques for AWSs. It analyzes the induced overvoltage characteristics as caused by the lightning with multiple return strokes on the signal cable of wind speed and direction, as well as their relationship with the changing rate of the triggered lightning current. The results indicate that the induced voltage peak of the signal line is in a V structure, with the crest value up to thousands of volts, and lasts only a few microseconds; and that a continuous voltage, which attenuates slowly, appears after the peak voltage, with the crest value up to hundreds of volts. The wind speed signal line has a higher induced voltage than the wind direction signal line does. The negative peak of the induced overvoltage on the signal line is well correlated with the gradient of the triggered lightning current, with the correlation coefficient being 0.70.

The artificially triggered lightning test was used and a 4-element AWS was simulated near the lightning channel to analyze and study the induced effects caused by the lightning and the key lightning protection techniques for AWS. This paper analyzes the induced overvoltage characteristics and SPD residue voltage characteristics caused by triggered lightning with multiple return strokes on the transmission line of an AWS, as well as the relationship with the triggered lightning. The results show that: (a) The return strokes of the near triggered lightning generate bipolar induced overvoltages on the overhead line, with peaks up to more than 10 kV. The overvoltages can be divided into the main peak phase and the subsequent overvoltage phase, which last about 100µs and 4ms respectively on average. The period of the subsequent overvoltages is related to the fluctuation of the current of the triggered lightning; (b) Overvoltages of 2kV or above can be induced at the initial continuous current phase. They last a long period of time and concentrate about 12ms, with the mean voltage being 332.5V. Its potential damage to the transmission line cannot be neglected.