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A strong and fast-moving electrical storm occurred in the Southwest Florida region overnight, from 01:00 UTC on 17 April to 07:00 UTC on 17 April 2023. Video recordings were conducted in the region at Latitude N 26.34° and Longitude W 81.79° for 5 h and 15 min, from 01:45 UTC to 07:00 UTC. The camera captured the flashes transforming from pinkish, violet, blue, and then emerald green in the sky twice: the first colored flash lasted 2.0 s, and the second one lasted 0.5 s. The characteristics of the flashes were analyzed using video images integrated with lightning flash data from the Geostationary Lightning Mapper (GLM). To gain deeper insights into the associated atmospheric conditions, the Advanced Baseline Imager (ABI) was also used to help understand the spectral anomalies. Both events had similarities: the same pattern of changing luminous colors in the optical images and the trajectory of the lightning discharges, showing clusters and horizontal distributions. Event 1 occurred mainly over the ocean and featured more intense storms, heavier rain, and denser, higher cloud-tops compared to Event 2, which occurred inland and involved dissipating storms. Moreover, the group energy detected in Event 1 was an order of magnitude higher than in Event 2. We attribute the wavelength of the recorded colored luminosity to varying atmospheric molecular concentrations, which ultimately contributed to the unique spectral line. In this study, we explore the correlation between colored flashes and specific atmospheric concentrations. [ABSTRACT FROM AUTHOR]

Pyrocumulonimbus (pyroCb) thunderclouds, produced from extreme bushfires, can initiate frequent cloud-to-ground (CG) lightning strikes containing extended continuing currents. This, in turn, can ignite new spot fires and inflict massive harm on the environment and infrastructures. This study presents a 3D numerical thundercloud model for estimating the lightning of different types and its striking zone for the conceptual tripole thundercloud structure which is theorized to produce the lightning phenomenon in pyroCb storms. More emphasis is given to the lower positive charge layer, and the impacts of strong wind shear are also explored to thoroughly examine various electrical parameters including the longitudinal electric field, electric potential, and surface charge density. The simulation outcomes on pyroCb thunderclouds with a tripole structure confirm the presence of negative longitudinal electric field initiation at the cloud's lower region. This initiation is accompanied by enhancing the lower positive charge region, resulting in an overall positive electric potential increase. Consequently, negative surface charge density appears underneath the pyroCb thundercloud which has the potential to induce positive (+CG) lightning flashes. With wind shear extension of upper charge layers in pyroCb, the lightning initiation potential becomes negative to reduce the absolute field value and would generate negative (−CG) lightning flashes. A subsequent parametric study is carried out considering a positive correlation between aerosol concentration and charge density to investigate the sensitivity of pyroCb electrification under the influence of high aerosol conditions. The suggested model would establish the basis for identifying the potential area impacted by lightning and could also be expanded to analyze the dangerous conditions that may arise in wind energy farms or power substations in times of severe pyroCb events. [ABSTRACT FROM AUTHOR]

The co-variability in the summer precipitation and cloud-to-ground lightning over South China, where climatological lighting and precipitation frequently occur (105～122 ° E, 20～35 ° N), has been examined using the ADTD lightning location network and precipitation data merged ground-gauge, satellite, and radar. The coupling self-organizing map (SOM) has been applied to the daily flash density and precipitation anomalies from 2016 to 2021. It turns out that there are five clusters associate with the co-variability in the flash density and precipitation over South China. Specifically, the first (fifth) cluster is characterized by a dipole pattern with enhanced rainfall / increased lightning activity (suppressed rainfall / decreased lightning activity) over the Yangtze-Huai River valley and suppressed rainfall/decreased lightning activity (enhanced rainfall/increased lightning activity) over the southern part of South China. The tightest lightning-precipitation coincidence is observed in the first and fifth clusters. Results obtained from SOM exhibit large non-linearity and asymmetry of the relationship between the regional lightning and precipitation anomalies over South China. Further examinations suggest that unstable atmospheric stratifications, significant vertical differences in the atmospheric humidity, and beneficial large-scale atmospheric circulations play important roles in modulating the co-variability in the summer lightning and precipitation over South China. [ABSTRACT FROM AUTHOR]

The development of cloud‐to‐ground (CG) lightning channel is one of the main bases reflecting the discharge characteristics. Time‐resolved spectra of CG lightning with eight return strokes were recorded by a slit‐less high‐speed spectroscope. We found an unusual phenomenon in which a branch developed upward from a node following a circling structure into the cloud after the first return stroke. To investigate the propagation properties of this lightning, characteristic parameters such as the two‐dimensional speed of the leader, node temperature, and electron density are analyzed. The physical mechanism of the branch is discussed. Spectral analysis reveals that the main channel temperature and electron density are approximately 2.72–3.07 × 104 K and 0.23–2.03 × 1018 cm−3, respectively. The temperature and electron density increase as the branch approaches the cloud base, similar to the feature of the main channel approaching the ground. The temperature and electron density of the node are higher than at other locations in the circular channel, indicating that massive charge accumulated around the node. Lightning occurred in the Qilian Mountains in a complex landscape, which easily yielded an uneven distribution in the local electric field of the air, resulting in channel bending, kinking, and even circle development. The phenomenon of the branch developed from the node to the cloud may be due to the fact that the branch is formed during the return stroke process. Plain Language Summary: The lightning channel does not usually continue to develop after the lightning return stroke is grounded. However, we discover an unusual phenomenon where the lightning leader formed a circular structure around a node on the main channel during its development. Immediately after the initiation of the first return stroke, a branch developed upward from the node into the cloud. To understand the reason why the branch developed from the node of the main cloud‐to‐ground lightning channel. Based on the time resolved spectra of the channel captured by a slit‐less high‐speed spectroscope, we analyze its physical characteristics, such as the two‐dimensional speed of the lightning leader, the temperature and electron density of the node, the main channel, and the branch channel. Our study found that this phenomenon may be related to the special geographical environment. Key Points: Rare phenomenon of CG lightning branch developed from a node on main channel upwards into the cloud was examined via spectral analysisTemperature and electron density slightly increased as branch channel approaching the cloud baseTemperature and electron density of leader tip reach the maximum when node formed [ABSTRACT FROM AUTHOR]

Lightning‐generated nitrogen oxides (LNOx) have an impact on the concentration of ground‐level ozone which acts as a toxic air pollutant, thereby negatively influencing human health and the environment. To understand the impact of LNOx on ground‐level ozone, we simulated four thunderstorm events in Tehran using the WRF‐Chem model. As observations of LNOx are not available, we evaluated the temporal distribution of the simulated ground‐level ozone concentration against an air quality monitoring station. We also compared the simulation results against the spatial distribution of the total column ozone from the Ozone Monitoring Instrument. WRF‐Chem performs well in the simulation of ground‐level ozone concentration, with the best performance for an event with the highest lightning activity (correlation coefficient of 0.91). The analysis of the spatial distribution of the observed and simulated total column ozone also indicates the good performance of WRF‐Chem. Hourly variation in the simulated LNOx during lightning activity is compared against both hourly variation in the observed ground‐level ozone and the number of lightning for four thunderstorm events. There is an agreement between the simulated LNOx and the observed ground‐level ozone during lightning for two events, with correlation coefficients of 0.55 and 0.57. LNOx emissions enhance ozone production in the middle to upper troposphere, which can subsequently contribute to an increase in ground‐level ozone by transport, vertical mixing, and chemistry. In addition, the initiation of chemical processes in response to cloud‐to‐ground lightning strikes may contribute to an increase in both LNOx and the concentration of ground‐level ozone. Plain Language Summary: Lightning‐generated nitrogen oxides (LNOx) contribute to higher ground‐level ozone, which acts as a harmful air pollutant for humans and the environment. We applied the WRF‐Chem model to simulate four thunderstorm events in Tehran, aiming to understand the impact of LNOx on ground‐level ozone concentration. Overall, WRF‐Chem performs well in the simulation of ground‐level ozone, particularly for an event with the highest lightning activity. The comparison of the spatial distribution of the observed and simulated total column ozone also indicates the good performance of WRF‐Chem. By comparing the simulated LNOx against the observed ground‐level ozone, we found that WRF‐Chem performs well for two thunderstorm events. The produced ozone in the middle to upper troposphere due to LNOx emissions can be transported downward and increase ground‐level ozone. Cloud‐to‐ground lightning strikes also contribute to an increase in both LNOx and ground‐level ozone pollution, which can negatively influence human health and the environment. Key Points: The simulated ground‐level ozone concentration is consistent with the observationThe initiation of chemical processes in response to cloud‐to‐ground lightning contributes to an increase in both LNOx and surface ozoneLNOx influence tropospheric ozone production, which can contribute to an increase in ground‐level ozone [ABSTRACT FROM AUTHOR]

A strong and fast-moving electrical storm occurred in the Southwest Florida region overnight, from 01:00 UTC on 17 April to 07:00 UTC on 17 April 2023. Video recordings were conducted in the region at Latitude N 26.34° and Longitude W 81.79° for 5 h and 15 min, from 01:45 UTC to 07:00 UTC. The camera captured the flashes transforming from pinkish, violet, blue, and then emerald green in the sky twice: the first colored flash lasted 2.0 s, and the second one lasted 0.5 s. The characteristics of the flashes were analyzed using video images integrated with lightning flash data from the Geostationary Lightning Mapper (GLM). To gain deeper insights into the associated atmospheric conditions, the Advanced Baseline Imager (ABI) was also used to help understand the spectral anomalies. Both events had similarities: the same pattern of changing luminous colors in the optical images and the trajectory of the lightning discharges, showing clusters and horizontal distributions. Event 1 occurred mainly over the ocean and featured more intense storms, heavier rain, and denser, higher cloud-tops compared to Event 2, which occurred inland and involved dissipating storms. Moreover, the group energy detected in Event 1 was an order of magnitude higher than in Event 2. We attribute the wavelength of the recorded colored luminosity to varying atmospheric molecular concentrations, which ultimately contributed to the unique spectral line. In this study, we explore the correlation between colored flashes and specific atmospheric concentrations.

Abstract Lightning‐generated nitrogen oxides (LNOx) have an impact on the concentration of ground‐level ozone which acts as a toxic air pollutant, thereby negatively influencing human health and the environment. To understand the impact of LNOx on ground‐level ozone, we simulated four thunderstorm events in Tehran using the WRF‐Chem model. As observations of LNOx are not available, we evaluated the temporal distribution of the simulated ground‐level ozone concentration against an air quality monitoring station. We also compared the simulation results against the spatial distribution of the total column ozone from the Ozone Monitoring Instrument. WRF‐Chem performs well in the simulation of ground‐level ozone concentration, with the best performance for an event with the highest lightning activity (correlation coefficient of 0.91). The analysis of the spatial distribution of the observed and simulated total column ozone also indicates the good performance of WRF‐Chem. Hourly variation in the simulated LNOx during lightning activity is compared against both hourly variation in the observed ground‐level ozone and the number of lightning for four thunderstorm events. There is an agreement between the simulated LNOx and the observed ground‐level ozone during lightning for two events, with correlation coefficients of 0.55 and 0.57. LNOx emissions enhance ozone production in the middle to upper troposphere, which can subsequently contribute to an increase in ground‐level ozone by transport, vertical mixing, and chemistry. In addition, the initiation of chemical processes in response to cloud‐to‐ground lightning strikes may contribute to an increase in both LNOx and the concentration of ground‐level ozone.

Pyrocumulonimbus (pyroCb) thunderclouds, produced from extreme bushfires, can initiate frequent cloud-to-ground (CG) lightning strikes containing extended continuing currents. This, in turn, can ignite new spot fires and inflict massive harm on the environment and infrastructures. This study presents a 3D numerical thundercloud model for estimating the lightning of different types and its striking zone for the conceptual tripole thundercloud structure which is theorized to produce the lightning phenomenon in pyroCb storms. More emphasis is given to the lower positive charge layer, and the impacts of strong wind shear are also explored to thoroughly examine various electrical parameters including the longitudinal electric field, electric potential, and surface charge density. The simulation outcomes on pyroCb thunderclouds with a tripole structure confirm the presence of negative longitudinal electric field initiation at the cloud’s lower region. This initiation is accompanied by enhancing the lower positive charge region, resulting in an overall positive electric potential increase. Consequently, negative surface charge density appears underneath the pyroCb thundercloud which has the potential to induce positive (+CG) lightning flashes. With wind shear extension of upper charge layers in pyroCb, the lightning initiation potential becomes negative to reduce the absolute field value and would generate negative (−CG) lightning flashes. A subsequent parametric study is carried out considering a positive correlation between aerosol concentration and charge density to investigate the sensitivity of pyroCb electrification under the influence of high aerosol conditions. The suggested model would establish the basis for identifying the potential area impacted by lightning and could also be expanded to analyze the dangerous conditions that may arise in wind energy farms or power substations in times of severe pyroCb events.

We present time‐correlated ultra‐high‐speed video camera and electromagnetic field measurements of the attachment processes in a natural negative cloud‐to‐ground stroke. The video camera frame exposure time and pixel resolution were 740 ns and 0.91 m/pixel, respectively. The common streamer zone (CSZ) was first observed 2.52 µs preceding the first frame showing the return stroke (RS) in progress, when the upward and downward leader‐tips were 9.8 m apart. In the next frame, the two leaders were observed to have propagated toward each other within the CSZ, with their tips being 0.91 m apart. Our observations show with unprecedented precision/clarity that (a) the slow front in the field waveform is associated with the CSZ, and (b) the "proper" start of the RS is marked by the onset of the fast transition in the field waveform which occurs at the completion of the attachment processes (when the upward and downward leaders have merged). Plain Language Summary: Detailed observations of how cloud‐to‐ground lightning attaches to ground remain very difficult to obtain. This is because the associated processes occur on a microsecond‐scale (or faster), making it challenging to perform time‐correlated multi‐instrument measurements. In this study, we present time‐correlated observations of ultra‐high‐speed video and electromagnetic fields, which provide new insights regarding the lightning attachment processes. These processes comprise the so‐called breakthrough phase of lightning attachment when two oppositely charged leaders (one from the thundercloud and one from ground or ground‐based object) merge with each other. Key Points: Time‐correlated multi‐sensor observations (with camera exposure time of 740 ns) of the natural lightning attachment processes were madeThe slow front portion of the field waveform is associated with the time‐evolution of the common streamer zoneFast‐transition onset in the field waveforms occurs when the upward and downward leaders fully merge ("proper" start of return stroke) [ABSTRACT FROM AUTHOR]

This paper demonstrates a 2-D numerical model to represent two conceptual pyrocumulonimbus (pyroCb) thundercloud structures: i) tilted dipole and ii) tripole structure with enhanced lower positive charge layer, which are hypothesized to explain the occurrence of lightning flashes in pyroCb storms created from severe wildfire events. The presented model considers more realistic thundercloud charge structures to investigate the electrical states and determine surface charge density for identifying potential lightning strike areas on Earth. Simulation results on dipole structure-based pyroCb thunderclouds confirm that the wind-shear extension of its upper positive (UP) charge layer by 2–8 km reduces the electric field and indicates the initiation of negative surface charge density around the earth periphery underneath the anvil cloud. These corresponding lateral extensions have confined the probable striking zone of –CG and +CG lightning within 0–23.5 km and 23.5–30 km in the simulation domain. In contrast, pyroCb thundercloud possessing the tripole structure with enhanced lower positive charge develops a negative electric field at the cloud's bottom part to block the progression of downward negative leader and cause the surface charge density beneath the thundercloud to become negative, which would lead to the formation of +CG flashes. Later, a parametric study is conducted assuming a positive linear correlation between the charge density and aerosol concentration to examine the effect of high aerosol concentration on surface charge density in both pyroCb thunderclouds. The proposed model can be expanded into 3-D to simulate lightning leader movement, aiding wildfire risk management.

A severe convective weather event occurred in the Arksu area of Xinjiang on 7 June 2017. In this event, two α-mesoscale convection systems (MCS) and their merging and development caused gale, hailstorm, and short-time heavy precipitation at several stations. The objective of this study is to determine the distribution characteristics of cloud-to-ground (CG) lightning and its relationship with cloud top brightness temperature (TBB) and the development of radar echo and convective system in this event, and to deepen the understanding of the characteristics of CG lightning activity. Using the lightning locating data over Xinjiang, the TBB data from FY-4A, the Doppler weather radar data, and other data, we conducted an analysis of the characteristics of CG lightning activity during this event. The results show that (1) the CG lightning activity concentrates on the warm advection side of the low-level shear line due to the obviously wetter lower and middle troposphere and the stability and continuance of the mesoscale shear line in the lower troposphere. (2) During the event, the CG lightning is mainly negative CG lightning, and its intensity is higher in the east and lower in the west of the Arksu area. There is a certain negative correlation between the CG lightning intensity and the CG lighting density. The large-scale strong wind near the ground has a strong linear correlation with the leap of CG lightning frequency and the decreasing of positive CG lightning proportion. (3) Most of CG lightning distributes in the areas where TBB is less than or equal to -40℃. The frequency of CG has positive and negative correlations with the cloud cluster areas with TBB ≤ -40℃ and the TBB minimum value, respectively. (4) During the period affected by MCS, most of the negative and positive CG lightning occur in the echo areas of 6-20 dBz and 11-15 dBz, respectively. Both the generation and development and the mature stages of convection, the peak value of vertical integrated liquid water content (VIL) appears 12-20 min earlier than the sharp increasing of CG lightning frequency. There are positive and negative correlations between CG lightning frequency and echo top height at the generation and development and the mature stages of convection, respectively.

Four years of Indian Institute of Tropical Meteorology lightning location network lightning observation data are used to determine the seasonal and spatial (over different geographical locations) distribution of the ratio of intra‐cloud (IC) lightning to cloud‐to‐ground (CG) lightning in thunderstorms over the Indian subcontinent. The ratio is high (6–10) in the northwestern parts and low (0.5–3.5) in the northeastern parts. No prominent latitudinal variation of the IC to CG ratio exists, but a climatological seasonal variability exists over all regions. In the pre‐monsoon season (March–May), the mean ratio is observed to be 3.81 with a standard deviation of 0.79, and during the monsoon season (June–September), a value of 3.04 with a standard deviation of 0.50. Although convective available potential energy is the regulating factor, little dependency has been found between the ratio of IC to CG lightning (IC:CG ratio) and the total flash rate (f), as well as with cold cloud depths. The ratio is observed to be proportional to the total flash rate as f0.61. The cold cloud depth is most prominently linked with the regional and seasonal IC:CG ratio. The implication of these observed results has the importance of separating CG lightning flash from total and can be used in numerical models to give a proper prediction of CG lightning in hazard mitigation. Plain Language Summary: Pre‐monsoon thunderstorms exhibit more intra‐cloud (IC) discharge than monsoonal thunderstorms; hence, the IC:cloud‐to‐ground (CG) ratio is also high in pre‐monsoon. In this paper, we have shown that CG lightning is approximately 20% of total lightning in pre‐monsoon whereas 25% of total lightning in monsoon all over the Indian region. A stronger vertical updraft associated with high convective available potential energy enhances the cold cloud depth. It may expand the mixed phase region, which can broaden and uplift the size of the upper positive charge center inside a thunderstorm. In contrast, the middle negative charge center remains at the same temperature level. Therefore, this process may enhance IC discharge between the upper positive charge center and the middle negative charge center, increasing the IC:CG ratio of a thunderstorm. Key Points: The mean intra‐cloud:cloud‐to‐ground (IC:CG) ratio remains high in the Pre‐monsoon season compared to the Monsoon season over the Indian land massThe high cold cloud depth associated with stronger updrafts expand the mixed‐phase region and increases the IC flash rate and IC:CG ratioHigh flash rate associated with high IC flash occurrences is also responsible for a high IC:CG ratio [ABSTRACT FROM AUTHOR]

Abstract We present time‐correlated ultra‐high‐speed video camera and electromagnetic field measurements of the attachment processes in a natural negative cloud‐to‐ground stroke. The video camera frame exposure time and pixel resolution were 740 ns and 0.91 m/pixel, respectively. The common streamer zone (CSZ) was first observed 2.52 µs preceding the first frame showing the return stroke (RS) in progress, when the upward and downward leader‐tips were 9.8 m apart. In the next frame, the two leaders were observed to have propagated toward each other within the CSZ, with their tips being 0.91 m apart. Our observations show with unprecedented precision/clarity that (a) the slow front in the field waveform is associated with the CSZ, and (b) the “proper” start of the RS is marked by the onset of the fast transition in the field waveform which occurs at the completion of the attachment processes (when the upward and downward leaders have merged).

Abstract Four years of Indian Institute of Tropical Meteorology lightning location network lightning observation data are used to determine the seasonal and spatial (over different geographical locations) distribution of the ratio of intra‐cloud (IC) lightning to cloud‐to‐ground (CG) lightning in thunderstorms over the Indian subcontinent. The ratio is high (6–10) in the northwestern parts and low (0.5–3.5) in the northeastern parts. No prominent latitudinal variation of the IC to CG ratio exists, but a climatological seasonal variability exists over all regions. In the pre‐monsoon season (March–May), the mean ratio is observed to be 3.81 with a standard deviation of 0.79, and during the monsoon season (June–September), a value of 3.04 with a standard deviation of 0.50. Although convective available potential energy is the regulating factor, little dependency has been found between the ratio of IC to CG lightning (IC:CG ratio) and the total flash rate (f), as well as with cold cloud depths. The ratio is observed to be proportional to the total flash rate as f0.61. The cold cloud depth is most prominently linked with the regional and seasonal IC:CG ratio. The implication of these observed results has the importance of separating CG lightning flash from total and can be used in numerical models to give a proper prediction of CG lightning in hazard mitigation.

Cloud-to-ground lightning can cause high-temperature and high-pressure deformation features in rock at the strike point, forming fulgurite. Although cloud-to-ground lightning is a frequent phenomenon, rock fulgurites are rarely reported. Here, we present field, optical microscope, X-ray fluorescence, scanning and transmission electron microscope, in situ synchrotron projection X-ray microscopy and X-ray diffraction, and Raman data to investigate the formation and preservation of a recently formed rock fulgurite from Kinmen Island, Taiwan. In the field, the fulgurite is asymmetrically distributed on the surface over an ~ 12 m2 area. In detail, the fulgurite contains an opaque glassy layer comprised of quartz and feldspar clasts, voids, iron-rich spheres, and barite aggregates that overlies fractured quartz grains and feldspar grains with planar features. Secondary minerals found locally adhering to the glassy layer as greenish patches are mainly jarosite group minerals, which commonly form as a secondary hydrothermal alteration product. We interpret the jarosite to have formed during the solidification of melt in the presence of raindrops, suggesting the rapid alteration of glass and short preservation potential of rock fulgurite. Finally, we estimate the production ratio of fulgurite by calculating the energy required for fulgurite formation and that released to the ground by the lightning event. A calculated energy ratio of 0.026% is within the range of 10–2 to 10–4 of the lightning total energy delivered to the strike point. We suggest that the scarcity of rock fulgurite in the geological record may be due to both the low production possibility and rapid alteration. [ABSTRACT FROM AUTHOR]

This research focuses on the climatology of cloud-to-ground (CG) lightning flashes based on PERUN lightning detection network managed by IMGW-PIB (Institute of Meteorology and Water Management – National Research Institute) during period 2002 to 2020. To present statistical data converted from raw lightning data, a grid cell with dimensions of 10 km × 10 km was used in order to standardize the results and refer to research conducted in other countries. As a result of the research, it can be concluded that the PERUN system detected 8,626,200 CG flashes during the 18-year period under study. Lightning data were used to determine the spatial distribution of CG flashes, number of thunderstorm days, the annual distribution or the hours of lightning occurrence. The average annual value of CG flashes varies from 0,5 to 3,5 flashes km−2·yr−1. The highest electrical activity occurs in central Poland (Mazovian Lowland) and the lowest in the Pomeranian Lake District. As a result of the research, it is possible to identify a storm trail that begins near Kraków-Częstochowa Upland and ends at the Masurian Lake District. The month with the highest electrical activity in Poland is July, while the highest electrical activity of thunderstorms occurred in 2017. Positive current flashes accounted for 4% of all detected CG flashes, with the greatest activity in June but since 2015, there has been visible increasing activity of thunderstorms carrying CG's with positive current. As a result of the analysis, it was also possible to identify a growing tendency of CG flashes in the area of whole country.

Lightning-generated electric field measurement is used to characterize cloud-to-ground (CG) flashes. Prior to the first return stroke (FRS), these signals sometimes exhibit a pulse train, known as preliminary breakdown pulses (PBP), whose study provides information about the first event that originate the breakdown process inside the cloud. Considering that characteristics of PBPs may change according to geographical conditions, in this work, six parameters (temporal and magnitude) associated with 69 trains identified in negative CG flashes that occurred in the Bogota savannah, Colombia were analyzed. The signatures were recorded in 2017 using a fast response antenna (10 MHz bandwidth), a 100 ns sampling time and a window of 500 ms. Among the most relevant results, it was found that the train duration ( ) varied from 0.5 ms up to 5.2 ms with arithmetic mean (AM) of 1.74 ms, while the time interval between the peak of the train and the FRS (PBP-FRS) had an AM and a geometric mean (GM) of 35.7 ms and 10.2 ms, respectively. On the other hand, the ratio between the peak value of the PBP and its FRS ( ) exhibited an AM of 0.7 and a GM of 0.56. It was concluded that PBP train starts with low amplitude pulses, later increases its magnitude in the central region and decreases at the end. Furthermore, bipolar pulses with similar polarity to that of the FRS were identified at the beginning and in the middle of the train, while unipolar pulses were observed at the end of the signatures.

This paper concerns eighty (80) lightning-ignited wildfires on Mount Mainalo, Greece, during the period from 1998 to 2022. Descriptive statistics of the dataset, frequency distribution histograms, and maps were used to describe the number of fires per year, the burned area per fire, the total burned area per year, the elevation of lightning-caused fire occurrences, the wildfire detection time, and the holdover time (the phase between the ignition and fire detection). The analysis shows an increased frequency of lightning-caused wildfires in August and July. Most of the fires took place in the southern part of the mountain and were detected in the afternoon hours. These preliminary findings and conclusions provide a comprehensive understanding of the past regime of natural fire on Mount Mainalo, and they can support improving wildfire prevention and management policies in the region.

Jiangsu Province is located in the middle coastal area of East China, and has a relatively developed economy and a large population density. Severe convection often occurs in Jiangsu Province, and the lightning activities may cause great economic losses and social impact in this region. Based on the theory of natural disaster risk assessment, this study investigates the risk of hazard factors, the sensitivity of hazard-pregnant environment, and the frangibility of a hazard-bearing body in Jiangsu Province. Then, we select thunderstorm days, cloud-to-ground (CG) lightning density, CG lightning current intensity, altitude, topographic relief, soil-electric conductivity, drainage density, population density, gross domestic product (GDP) per land area, and soil utilization type as the influencing factors, and then we use the analytic hierarchy process and entropy weight method to calculate the weights of the influencing factors. Furthermore, all the factors are weighted stacked in ArcGIS, and finally the lightning disaster risk zoning map (1 × 1 km of Jiangsu Province is presented. The results show that the risk of lightning disaster in Jiangsu is low in the north and high in the south. The area of different risk level increases with the decrease in risk level. High-risk areas are mainly in the middle of Nanjing, eastern Changzhou, eastern Wuxi, and the middle of Suzhou. Medium-risk areas are mainly in northern Nanjing, eastern Changzhou, eastern Suzhou, the Tongshan District of Xuzhou City, the Chongchuan District of Nantong City, Lianyun District of Lianyungang City, and the Xiangshui County, Sheyang County, and Dafeng District of Yancheng City. The sub–low-risk areas are mainly in Xuzhou, Suqian, Huai’an, and the middle of Yangzhou City. The low-risk areas are mainly in Lianyungang, Yancheng, northern Nantong, Taizhou, Zhenjiang, southern Nanjing, western Changzhou, western Wuxi, and western Suzhou. We hope this study could provide some references for the lightning disaster prevention and mitigation in Jiangsu Province and East China.

The spatiotemporal distribution of cloud-to-ground (CG) lightning activities on the Yungui Plateau is investigated in this study by using a 5-year dataset (2016–2020) from the ground-based National Lightning Detection Network (CNLDN). The correlations between the lightning activities and different meteorological factors in the region are also analyzed. The results show that there is an obvious difference in the spatial distribution of lightning activities on the Yungui Plateau during the 5 years, with high lightning density in the east and low lightning density in the west. The lightning activities shift and gather more towards the eastern plateau especially after 2019. Affected by the quasi-stationary front in Kunming, the spatial distributions of lightning flashes in cold and warm seasons are different. On the other hand, the frequency of the lightning activities varies from year to year, such as the surge in 2019. But in general, 62% of the lightning activities are produced in summer and the lightning flashes occur more often in the afternoon and evening on the Yungui Plateau. Additionally, it is found that lightning activities in the 5 years are closely related to precipitation and temperature, while there is a weak correlation with relative humidity and almost no correlation with sensible heat flux. The analysis also indicates that the CAPE×P (convective available potential energy times precipitation rate) proxy can be effectively used to describe and predict lightning activities on the Yungui Plateau as the lightning flashes corresponds well to CAPE×P, especially of the spatial distribution.

Lightning matters to human life and natural fires so much that monitoring and predicting lightning are highly important. A simple proxy for climatic cloud‐to‐ground (CG) density is evaluated defined as the product of convective available potential energy (CAPE) and precipitation rate using data from 2005 to 2017 in Sichuan of Southwest China. CAPE times precipitation rate (CP) relates the monthly distribution and magnitude of negative lightning in the basin region more closely, while CP describes the monthly distribution and magnitude of positive lightning in the plateau region more appropriately. Except for individual years, the annual variation trend and magnitude of CP and positive and negative lightning are relatively consistent in the basin region, while the description of the annual variation trend and magnitude of lightning by CP in the plateau region is insufficient, especially for negative lightning. CP represents the high‐value areas of the positive and negative lightning in the basin and southern Sichuan reasonably, but misses the lightning belt in the plateau region. In general, the performance of CP for lightning in the basin is superior to that in the plateau, this may be caused by two factors, one is the particularity and complexity of lightning in the plateau resulted from special topographic and meteorological conditions, the other one is the limitation of CP caused by the fact that CP does not take into account other environmental factors contributing to lightning. The ability of this simple proxy to describe CG lightning in Sichuan is limited by vertical wind shear in the middle and lower troposphere, zero degree height, and liquid water path, mainly because the proxy does not have the ability to generalize these factors that play a key role in lightning activity. [ABSTRACT FROM AUTHOR]

Lightning activity could be an indicator of the occurrence of a tornado. Based on lightning location data, Doppler radar data, sounding data and ECMWF reanalysis data, the spatio-temporal evolution of cloud-to-ground (CG) lightning, the intensity of lightning current and the features of positive CG lightning in two typical severe tornado storms are analyzed. The results show that CG lightning mainly occurs in the area with composite reflectivity greater than 30 dBZ. When tornadoes occur, CG lightning activities decrease and are relatively dispersed. Due to the different intensities of updrafts, CG lightning frequencies vary greatly in different tornado storms. Tornadoes touch down during the period when CG lightning frequency decreases from the maximum to the minimum. In the two cases, the maximum frequency of CG lightning appears 33 minutes and 28 minutes ahead of the tornado occurrence. Before tornadoes touch down, there are several lightning jumps. Moreover, the higher the tornado event level, the more positive CG lightning occurs, and the more obvious the positive CG lightning characteristics are. A CG lightning polarity reversal from positive-dominated to negative-dominated happens during the tornado episode in Funing County, Yancheng City. Within the lifecycles of the two tornadoes, the lightning current intensity does not vary significantly and is smaller than the historical mean. It is found that the more frequently CG lightning occurs in tornado storms, the smaller the lightning current intensity will be. [ABSTRACT FROM AUTHOR]

From January 2020 to December 2021, Ulanqab Meteorological Bureau of Inner Mongolia used VLF/LF lightning locator to carry out three-dimensional lightning monitoring in Ulanqab City, and compared with ADTD lightning location data in the same period. The results show that both VLF/LF lightning locator and ADTD lightning locator had excellent monitoring ability for lightning during flood season in Ulanqab. VLF/LF lightning locator was slightly superior to ADTD lightning locator in observation accuracy, the observation ability of low-current cloud-to-ground lightning, intracloud lightning observation and so on. There were obvious temporal and spatial characteristics of cloud-to-ground lightning during flood season in Ulanqab, and there was a certain correlation between the areas where lightning appeared frequently and surface water. Intracloud lightning was mainly concentrated at a height of 1-7 km. Negative cloud-to-ground lightning accounted for about 75% of total cloud-to-ground lightning, and negative intracloud lightning accounted for 39% of total intracloud lightning. [ABSTRACT FROM AUTHOR]

This research focuses on the spatial diversity of cloud-to-ground (CG) flashes in the Kujawsko-Pomorskie voivodeship (Poland) based on data from the PERUN lightning detection system, 2002-2019. The storm season usually lasts from May to September, with July having the highest number of thunderstorms days and flashes. Thunderstorms most often occur in the afternoon. A generated grid of 5×5-km cells was used to characterise the variables related to CG flashes. In the analysed period 432,925 CG flashes were detected in the voivodeship (24,051 flashes year-1). The highest electrical activity was found in the south-eastern part of the province. In grids with a large water surface, the number of CG flashes was small and increased with distance from the Vistula River. The distribution of atmospheric discharges in major cities of the region (Bydgoszcz, Toruń, Włocławek and Grudziądz) was random. Years with greater electrical storm activity (27,614 discharges in 2017) are interspersed with calmer years (5000-7000 discharges). There were found an upward trend in lightning discharges (of 1681 discharges year-1) during period 2002-2019. To develop maps specifying the number of thunderstorm days, a 1×1-km grid cell was used with a 15-km radius buffer from the bin centre. The annual number of thunderstorm days in the voivodeship fluctuates from 27 to 41 days and increases from north-west to south-east. Consecutive days with a thunderstorm, the most common runs are of three days in a row with a storm. The number of thunderstorm days shows an increasing trend (0.82 days year-1). This trend is related to the increase in air temperature in the storm season (Apr-Sep) reaching (0.04°C year-1). [ABSTRACT FROM AUTHOR]

This research documents atmospheric conditions and development of high electrically active thunderstorm days that occurred over Poland in period 2002–2020. The 8 days with the highest number of detected cloud-to-ground flashes during one storm cell life cycle were analyzed. The study used data from the PERUN lightning detection and location system, ERA5-reanalysis, vertical atmospheric soundings, and synoptic maps as well. As a result of the analysis, it can be concluded that the development of thunderstorms is positively influenced by the low-pressure area above the North Sea and the atmospheric fronts with zone of wind convergence in the lower troposphere. The analyzed storm systems on the analyzed days were created in the atmosphere of a high vertical wind shear (from 10 to 18 m s−1), lifted index (from +0.04 to –8.22), thermodynamic instability (CAPE 1000–3700 J kg−1), rich boundary layer moisture (mixing ratio: 12–14 g kg−1), and high tropospheric moisture (total column water vapour >50 kg m−2). Very moist air masses ahead of the storm systems provided consistent access to large amounts of latent heat released into the clouds and intensified upward mass fluxes and development of intense lightning activity from Cumulonimbus cloud.

Abstract We present sub‐microsecond‐scale, high‐speed video camera observations of three negative stepped leaders in cloud‐to‐ground flashes with return‐stroke peak currents (estimated by the U.S. National Lightning Detection Network) of −17, −104, and −228 kA. The camera frame exposure times for these observations were 1.8, 1.0, and 0.74 µs, respectively. The 0.74 µs exposure time is the shortest reported to date. We observed the temporal and spatial evolution of space leaders from their inception to their attachment to the pre‐existing leader channel (PELC). For stepped leaders that led to return strokes having higher peak currents, the space leaders appear to have incepted at farther median two‐dimensional distances from their respective PELC‐attachment points. These median distances were 6.1, 16.6, and 17.6 m, respectively, for the three strokes. Our observations indicate that space leader characteristics are likely influenced by stepped‐leader line‐charge‐density, which is expected to be higher in strokes with higher return‐stroke peak currents.

We present sub‐microsecond‐scale, high‐speed video camera observations of three negative stepped leaders in cloud‐to‐ground flashes with return‐stroke peak currents (estimated by the U.S. National Lightning Detection Network) of −17, −104, and −228 kA. The camera frame exposure times for these observations were 1.8, 1.0, and 0.74 µs, respectively. The 0.74 µs exposure time is the shortest reported to date. We observed the temporal and spatial evolution of space leaders from their inception to their attachment to the pre‐existing leader channel (PELC). For stepped leaders that led to return strokes having higher peak currents, the space leaders appear to have incepted at farther median two‐dimensional distances from their respective PELC‐attachment points. These median distances were 6.1, 16.6, and 17.6 m, respectively, for the three strokes. Our observations indicate that space leader characteristics are likely influenced by stepped‐leader line‐charge‐density, which is expected to be higher in strokes with higher return‐stroke peak currents. Plain Language Summary: Lightning and thunderstorm activity have extremely important socio‐economic impacts including on power transmission and distribution, severe weather prediction, lightning safety and protection, management of outdoor events, airport and maritime activities, air travel, and space launches. The vast majority of lightning occurring between thunderclouds and the Earth's surface effectively transfer negative charge to ground. In such discharges, the first negatively charged channel (called a leader) proceeds from the thundercloud to ground in a stepwise fashion, pausing for fractions of a second after each step, before reaching ground. Many questions remain about the detailed mechanism of negative cloud‐to‐ground stepped‐leader progression and how natural lightning leaders compare to those in long sparks in laboratory experiments. We observed sub‐microsecond‐scale processes that lead to the formation and progression of negative cloud‐to‐ground lightning leader channels. Our study presents a detailed characterization of space leaders, a region of super‐heated plasma just ahead of the negative leader tip, that forges a path forward for the first stroke in cloud‐to‐ground lightning. Results of this study help explain why negative leaders pause between bursts of rapid acceleration. Key Points: Median space‐leader maximum 2‐D lengths and inception‐to‐attachment‐point distances are longer in higher peak‐current return strokesHigher stepped‐leader line‐charge‐densities in strokes with higher return‐stroke peak currents influence space‐leader characteristicsLeader‐step lengths and speeds are affected by the varying electric field environments at different altitudes above ground [ABSTRACT FROM AUTHOR]

• Positive cloud-to-ground flashes recorded at 23 locations in the Austrian Alps. • Dataset contains 107 positive Cloud-to-Ground (+CG) flashes including 121 strokes. • 11 multi-stroke +CG flashes including 3 rarely observed single-channel flashes. • 90 % single-stroke flashes, median return stroke peak current 47.4 kA. • Mean duration for 67 continuing currents of the 121 strokes 126.1 ms. Flashes with positive polarity, representing about 10 % of all cloud-to-ground flashes, were analyzed for this publication. Data from positive cloud-to-ground flashes recorded in the Austrian Alps over five years from 2015 to 2022 were used. The measurements were performed to record ground truth flash data at 23 selected locations and to compare their characteristics with values from the literature. The used measurement system consists of a high-speed Video camera and an electric Field Recording System (VFRS). Data of both systems are correlated with Lightning Location System (LLS) data by using a GPS time stamp. The overall dataset showed 107 positive flashes, comprising 121 strokes (11 multi-stroke flashes). The percentage of positive single-stroke flashes is 90 % for VFRS data and 84 % for LLS data. The mean multiplicity for VFRS data is 1.1. The LLS estimated median return stroke peak current of all analyzed positive strokes is 47.4 kA. The mean duration for 67 continuing currents of the 121 strokes is 126.1 ms. The detection efficiency of correctly detected positive flashes and strokes is 96.3 % and 89.3 %, respectively. A better understanding of positive flashes in general and in the Alpine region in particular shall be provided by the presented results. [ABSTRACT FROM AUTHOR]

This article puts forward an algorithm for estimating the detection efficiency (DE) of a lightning location system (LLS). The algorithm can be applied to lightning flash/stroke density correction and LLS performance evaluation. Fundamentally, the generalized extreme value (GEV) distribution was found to best fit the probability distribution of the signal strengths of the lightning observed by the ADvanced TOA and Direction system (ADTD) detectors in Beijing, China. With respect to this probability distribution, we estimated the single-station acceptance damped by the uneven underlying land surface conductivity, which is determined by overlapping the soil-type polygons with the propagating paths of electromagnetic lightning signals. Accounting for the multi-detector location modes supported by single-station acceptance, the iterative algorithm was applied for deducing the network DE. In this case study, the DE estimates were lower in the mountainous areas than in the plains. This can be due to the low underlying conductivity of the mountainous areas, which creates a high attenuation effect on the lightning electromagnetic signals, and the greater distances from the lightning detectors. The CG lightning flash/stroke density corrected for the DEs revealed that the CG lightning flash/stroke densities in the mountains are lower than that in the highly urbanized plains.

Storms and their associated phenomena have a high impact in a country's social and economic environment. It is necessary to have tools that guarantee the safety of people at all times. The data provided by a network of meteorological radars is of utmost importance for storm tracking and identification. These radar networks are expensive and difficult to maintain. Not all countries have a radar network that covers all its extension and even so, they often have technical or connectivity problems that leave large areas without information about rainfall. In this work we present a technique to generate a synthetic radar reflectivity field using supervised deep learning techniques with cloud-to-ground lightning data. This product can be used as a cost-effective radar alternative in areas where there is no or poor coverage, or as a complement to meteorological radar images that are affected by attenuation, interference or other observation problems. [ABSTRACT FROM AUTHOR]

Oceanic lightning can be a sensitive indicator of aerosol effects on lightning characteristics as thermodynamic contrast is indistinct over adjacent oceanic regions. The study presents discernable aerosol impacts on lightning characteristics by analyzing 2 years (2017–2018) of intracloud (IC) and cloud‐to‐ground (CG) lightning data from Earth Networks Total Lightning Network over two key regions in southern South China Sea. Mean stroke density, IC/CG ratio, +IC fraction, and +CG fraction in polluted conditions are respectively 3.7, 2, 1.2, and 5.8‐fold larger than unpolluted counterparts. Total stroke contrast is further confirmed with the GLD360 network. Thermodynamic parameters conversely support slightly stronger convection over clean ocean. Clear evidence shows cloud droplet size diminishes with added aerosol. Aerosol invigorates more frequent and robust mixed‐phase development, endowing maritime convection with continental characteristics. Modifications in the charge reversal temperature and lower and upper positive charge regions are speculated on as means for stimulating more positive ICs and CGs. Plain Language Summary: Over adjacent oceanic regions, the thermodynamic contrast is indistinct, and this makes oceanic lightning a sensitive indicator of aerosol effects. The southern South China Sea, surrounded by wideband electric‐field sensors in Earth Networks Total Lightning Network, is focused on the response of both intracloud (IC) and cloud‐to‐ground (CG) strokes to added aerosol over 2 years (2017–2018). The thermodynamic and cloud microphysical parameters are quantitatively analyzed between polluted and clean oceanic regions. Distribution maps of sulfur dioxide and aerosol optical depth show clear locations for polluted regions. Mean stroke density, IC/CG ratio, +IC fraction, and +CG fraction in polluted conditions are respectively 3.7, 2, 1.2, and 5.8‐fold larger than the unpolluted counterparts, while thermodynamic parameters conversely support slightly weaker convection over polluted regions and discount its effects in supporting lightning enhancement. Added aerosol decreases cloud effective particle radius of ice and liquid water based on satellite measurement. Larger lower and upper positive charge reservoirs invigorated by the energized graupel‐ice crystal electrification process and possible modification of the charge reversal temperature are speculated as mechanisms to promote more positive strokes. More frequent and robust mixed‐phase development favorable for lightning is stimulated by added aerosol over ocean, endowing maritime convection with continental characteristics. Key Points: Oceanic lightning can be a sensitive indicator of aerosol effects on lightning characteristics as the thermodynamic contrast is indistinct or even supports weaker convection in the polluted regionMean stroke density, IC/CG ratio, +IC fraction, and +CG fraction in the polluted oceanic region are respectively 3.7, 2, 1.2, and 5.8 ‐fold larger than the adjacent unpolluted oceanic counterpartsAerosol provides for more frequent and robust mixed‐phase development, endowing maritime convection with continental characteristics [ABSTRACT FROM AUTHOR]

The radiated electric field produced by lightning plays a vital role in lightning location systems (LLSs). The presence of the elevated objects, i.e. transmission lines in the presented study, result in an increase of amplitude and multiple sub‐peaks in the observed electric fields. On the basis of the electric fields obtained from multiple sensors of Foshan total LLS, electric fields from nine negative lightning strokes associated with transmission‐line faults at a distance of 10–86 km in Foshan area were examined in detail, which were adopted to make comparison with the radiated electric fields from natural negative cloud‐to‐ground lightning detected nearby within 1 min. It can be found that the arithmetic means (AMs) of initial electric‐field peak values of waveforms associated with transmission‐line faults are about twice those of natural negative lightning and the second and third sub‐peaks can be identified obviously. In addition, the correlation between electric‐field waveform characteristics and propagation distance was validated. The AM zero‐crossing time, fast‐transition 10–90% rise time and the time interval between sub‐peaks slightly increase with distance. [ABSTRACT FROM AUTHOR]

The effect of aerosols on lightning has been noted in many studies, but much less is known about the long-term impacts in air-polluted urban areas of China. In this paper, 9-year data sets of cloud-to-ground (CG) lightning, aerosol optical depth (AOD), convective available potential energy (CAPE), and surface relative humidity (SRH) from ground-based observation and model reanalysis are analyzed over three air-polluted urban areas of China. Decreasing trends are found in the interannual variations of CG lightning density (unit: flashes km−2day−1) and total AOD over the three study regions during the study period. An apparent enhancement in CG lightning density is found under conditions with high AOD on the seasonal cycles over the three study regions. The joint effects of total AOD and thermodynamic factors (CAPE and SRH) on CG lightning density and the percentage of positive CG flashes (+CG flashes/total CG flashes × 100; PPCG; unit: %) are further analyzed. Results show that CG lighting density is higher under conditions with high total AOD, while PPCG is lower under conditions with low total AOD. CG lightning density is more sensitive to CAPE under conditions with high total AOD.

Sprites are transient luminous events (TLEs) that occur over thunderstorm clouds that represent the direct coupling relationship between the troposphere and the upper atmosphere. We report the evolution of a mesoscale convective system (MCS) that produced only one sprite event, and the characteristics of this thunderstorm and the related lightning activity are analyzed in detail. The results show that the parent flash of the sprite was positive cloud-to-ground lightning (+CG) with a single return stroke, which was located in the trailing stratiform region of the MCS with a radar reflectivity of 25 to 35 dBZ. The absolute value of the negative CG (−CG) peak current for half an hour before and after the occurrence of the sprite was less than 50 kA, which was not enough to produce the sprite. Sprites tend to be produced early in the maturity-to-dissipation stage of the MCS, with an increasing percentage of +CG to total CG (POP), indicating that the sprite production was the attenuation of the thunderstorm and the area of the stratiform region.

This article puts forward an algorithm for estimating the detection efficiency (DE) of a lightning location system (LLS). The algorithm can be applied to lightning flash/stroke density correction and LLS performance evaluation. Fundamentally, the generalized extreme value (GEV) distribution was found to best fit the probability distribution of the signal strengths of the lightning observed by the ADvanced TOA and Direction system (ADTD) detectors in Beijing, China. With respect to this probability distribution, we estimated the single-station acceptance damped by the uneven underlying land surface conductivity, which is determined by overlapping the soil-type polygons with the propagating paths of electromagnetic lightning signals. Accounting for the multi-detector location modes supported by single-station acceptance, the iterative algorithm was applied for deducing the network DE. In this case study, the DE estimates were lower in the mountainous areas than in the plains. This can be due to the low underlying conductivity of the mountainous areas, which creates a high attenuation effect on the lightning electromagnetic signals, and the greater distances from the lightning detectors. The CG lightning flash/stroke density corrected for the DEs revealed that the CG lightning flash/stroke densities in the mountains are lower than that in the highly urbanized plains. [ABSTRACT FROM AUTHOR]

The spectra of cloud-to-ground lightning return strokes channels are obtained by a slit-less high-speed spectrograph. Based on the positive correlation between discharge current and the intensity of ionic lines in the spectra, variation characteristics of return stroke current along the discharge channel are investigated. The result shows that there are three types of the variation trend for discharge current with the increase of height along the channel, they are exponential attenuation, linear attenuation and basically unchanged, respectively. The attenuation factor is roughly positive correlated with the discharge intensity. During strong discharge process the current tends to decay exponentially. In addition, during return stroke process, the current attenuation gradually flattens with time. • The attenuation law of return stroke current along the channel is investigated according to the spectra. • The current decay along the channel presents three trends: exponential decay, linear decay and basically unchanged. • The current tends to decay exponentially during strong discharge process. [ABSTRACT FROM AUTHOR]

We developed a new method to distinguish the lightning discharge type using lightning data obtained by JEM-GLIMS spaced-based mission and ground-based lightning network that are JLDN, NLDN, WWLLN, and GEON. As a first step, we selected 1057 lightning events detected by the JEM-GLIMS cameras (LSI) and spectrophotometers (PH) in 2014. Then, we compared the JEM-GLIMS optical data to the ground-based lightning data in order to check the simultaneous detection of JEM-GLIMS lightning events by the ground-based lightning networks, and finally we identified the discharge type of the JEM-GLIMS lightning events. We succeed in identifying 941 simultaneous lightning events and found that 582, 93, and 266 lightning events were IC, +CG, and -CG discharges, respectively. As a next step, we calculated intensity ratios between blue and red PH channels, i.e., 337nm/762 nm, 316nm/762 nm, 392nm/762 nm, 337nm/(599–900 nm), 316nm/(599–900 nm), and 392nm/(599–900 nm) for the 941 lightning events in order to specify the optical characteristics of IC, +CG, and -CG discharges. It is found that the PH intensity ratio of +CG discharges is the highest and that the PH intensity ratio of IC and -CG discharges is smaller than that of +CG discharge. We also found that the characteristics of the LSI intensity ratio are almost comparable to those of the PH intensity ratio. As the differences of the 337nm/762 nm, 337nm/(599–900 nm), and 392nm/(599–900 nm) ratio of IC, +CG, and -CG discharges are relatively large, these three ratios are a useful proxy for classifying the discharge types for additional 7349 lightning events detected by JEM-GLIMS in order to estimate the global ratio between IC and CG discharges (Z ratio). • Method to distinguish the lightning discharge type using JEM-GLIMS optical data is newly developed. • The PH intensity ratio and the LSI intensity ratio of IC discharges are different from those of +CG and -CG discharges. • The PH2/PH3, PH2/PH4 and PH6/PH4 ratio are the useful proxy to distinguish the discharge types. [ABSTRACT FROM AUTHOR]

To investigate the possible impact of urban development on lightning activity, an eight-year (2010–2017) cloud-to-ground (CG) lightning dataset provided by the National-Wide Lightning Detection Network in China was analyzed to characterize the CG lightning activity in the metropolitan area of Beijing. There is a high CG flash density area over the downtown of Beijing, but different from previous studies, the downwind area of Beijing is not significantly enhanced. Compared with the upwind area, the CG flash density in the downtown area was enhanced by about 50%. Negative CG flashes mainly occurred in the downtown and industrial area, while positive CG flashes were distributed evenly. The percentage of positive CG flashes with Ipeak ≥ 75 kA is more than six times that of the corresponding negative CG flashes in the Beijing area. The enhancement of lightning activity varies with season and time. About 98% of CG flashes occurred from May to September, and the peak of CG diurnal variation is from 1900 to 2100 local time. Based on the analysis of thunderstorm types in Beijing, it is considered that the abnormal lightning activity is mainly responsible for an enhancement of the discharge number in frontal systems rather than the increase of the number of local thunderstorms. In addition, there is a non-linear relationship between pollutant concentrations and CG flash number, which indicates that there are other critical factors affecting the production of lightning.

We analyzed currents associated with upward connecting leaders (UCLs) initiated from the Kennedy Space Center Industrial Area Tower in two negative cloud-to-ground strokes that struck the tower. One stroke was also recorded using a high-speed video camera located 760 m from the KSC IAT. The NLDN-reported peak currents for the two strokes were − 31.7 and − 98.5 kA. During the UCL development phase the current waveforms exhibited a monotonically (quasi-exponentially) increasing "background" current overlaid with 10-μs scale pulses with a median amplitude of 51.1 A. The UCL current durations for the two strokes were 1039 and 449 μs, respectively. During the pre-attachment processes (UCL and slow front) the total negative charge effectively transferred to ground were 70.2 and 55 mC, respectively. For the stroke captured on high-speed video, the average line-charge-density for the 109-m long UCL was found to be 0.5 mC/m. The average UCL 2-D speed was 2.4 × 105 m/s, and it was observed to accelerate toward the downward leader prior to attachment. We observed that UCL-pulse amplitudes are larger, background currents are higher, and interpulse intervals are shorter at later times during UCLs, which can be attributed to the intensification of the local electric field due to the approaching downward negative leader. The median positive charge injected into the UCL by a pulse was 297 μC. The UCL associated with the higher peak-current stroke produced the highest injected pulse-charge values about three times sooner during its development, likely due to the 2–2.7 times faster average downward leader vertical speeds. • We measured upward connecting leader (UCL) current durations of 1039 and 449 μs. • We computed an average line-charge-density of 0.5 mC/m for a 109-m long UCL. • UCL was observed to accelerate toward the downward leader prior to attachment. • Median pulse amplitude and pulse-charge were larger for UCLs than those for UULs. [ABSTRACT FROM AUTHOR]

Wildland fires exert substantial impacts on tundra ecosystems of the high northern latitudes (HNL), ranging from biogeochemical impact on climate system to habitat suitability for various species. Cloud-to-ground (CG) lightning is the primary ignition source of wildfires. It is critical to understand mechanisms and factors driving lightning strikes in this cold, treeless environment to support operational modeling and forecasting of fire activity. Existing studies on lightning strikes primarily focus on Alaskan and Canadian boreal forests where land-atmospheric interactions are different and, thus, not likely to represent tundra conditions. In this study, we designed an empirical-dynamical method integrating Weather Research and Forecast (WRF) simulation and machine learning algorithm to model the probability of lightning strikes across Alaskan tundra between 2001 and 2017. We recommended using Thompson 2-moment and Mellor–Yamada–Janjic schemes as microphysics and planetary boundary layer parameterizations for WRF simulations in the tundra. Our modeling and forecasting test results have shown a strong capability to predict CG lightning probability in Alaskan tundra, with the values of area under the receiver operator characteristics curves above 0.9. We found that parcel lifted index and vertical profiles of atmospheric variables, including geopotential height, dew point temperature, relative humidity, and velocity speed, important in predicting lightning occurrence, suggesting the key role of convection in lightning formation in the tundra. Our method can be applied to data-scarce regions and support future studies of fire potential in the HNL.

The spatial-temporal patterns of cloud-to-ground (CG) lightning covering the period 2010-2015 over the northwest Iberian Peninsula were investigated. The analysis conducted employed three main methods: the circulation weather types developed by Jenkinson and Collison, the fit of a generalized additive model (GAM) for geographic variables, and the use of a concentration index for the ratio of lightning strikes and thunderstorm days. The main activity in the summer months can be attributed to situations with eastern or anticyclonic flow due to convection by insolation. In winter, lightning proves to have a frontal origin and is mainly associated with western or cyclonic flow situations which occur with advections of air masses of maritime origin. The largest number of CG discharges occurs under eastern flow and their hybrids with anticyclonic situations. Thunderstorms with greater CG lightning activity, highlighted by a higher concentration index, are located in areas with a higher density of lightning strikes, above all in mountainous areas away from the sea. The modeling of lightning density with geographic variables shows the positive influence of altitude and, particularly, distance to the sea, with nonlinear relationships due to the complex orography of the region. Likewise, areas with convex topography receive more lightning strikes than concave ones, a relation which has been demonstrated for the first time from a GAM. [ABSTRACT FROM AUTHOR]

Based on cloud-to-ground lightning data of lightning location system, Doppler radar data, and precipitation data of regional automatic weather stations, the characteristics of cloud-to-ground lightning during a local rainstorm on June 4, 2016 in Meizhou City were analyzed. Theresults showed that the spatial distribution of cloud-to-ground lightning from 14:00 to 20:00 on June 4, 2016 in Meizllou City had obvious local charaoteristics, and the proportion of negative lightning was larger than that of positive lightning (only 16.8%). The concentration period of positive lightning coincided with that of cloud-to-ground lightning. The peak of proportion of positive lightning lagged behind the peak of cloud-to-ground lightning, and appeared in the late period of thunderstorm disappearance. The dense area of cloud-to-ground lightning and the area with heavy rainfall coincided with the area with strong radar echoes. Doppler weather radar data had the feature of the headwind zone, strong combined reHectivity, vertical height of strong echoes, high echo top, and fast radial movement. The peak of cloud-to-ground lightning appeared one hour earlier than that of precipitation. There was no significant correlation between the frequency of cloud-to-ground lightning and precipitation. The peak of negative lightning corresponded to that of positive lightning, and cloud-to-ground lightning ended earlier than rainfall. After the peak of precipitation, convective system rapidly weakened and disappeared. Precipitation and the frequency of cloud-to-ground lightning fluctuated frequently during the whole process. The jumps and peeks of negative lightning were indicative of rainfall changes. [ABSTRACT FROM AUTHOR]