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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 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]

On 10 July 2015, a cloud-to-ground (CG) lightning flash that produced two ground terminations was photographed from inside the safety of a truck in southern New Mexico. An analysis of archived NLDN data verified that this was a two-stroke flash, and a close-up view of the first stroke shows that it also initiated at least 12 unconnected, upward leaders (or “streamers”) near the ground termination. No unconnected upward leaders were seen near the second ground attachment. After combining an analysis of the photograph with information provided by the NLDN, we infer that the first stroke was of negative (normal) polarity, had modest peak current, and struck about 460 m (± 24%) from the camera. Attachment occurred when an upward-propagating positive leader reached an inferred height of about 21 m above local ground. The second stroke struck ground about 740 m from the camera, and the height of its attachment leader is estimated to be 15 m. The estimated lengths of the unconnected upward leaders in the two-dimensional (2-D) plane of the first stroke range from 2 to 8 m, and all appear to be located within 15 m (2-D) of the main ground termination, with 24% uncertainty. Many of the unconnected upward leaders (inferred to be positive) exhibit multiple upward branches, and most of those branches have upward-directed forks or splits at their ends. This is the first report showing such extensive branching for positive upward leaders in natural lightning strikes to ground. None of the upward leaders can be seen to emanate from the tops of tall, isolated, or pointed objects on the ground, but they likely begin on small plants and rocks, or flat ground. In terms of lightning safety, this photo demonstrates that numerous upward leaders can be produced near a lightning strike point and have the potential to damage or cause injury at more than one specific point on the ground. [ABSTRACT FROM AUTHOR]

Cloud-to-ground (CG) lightning, meteorological conditions and corresponding surface nitrogen oxides (NO x ) and ozone (O 3 ) variations in relation to thunderstorm and lightning activities over Hong Kong at Kwai Chung (urban), Tung Chung (new town) and Tap Mun (background) during active lightning seasons from 2009 to 2013 were studied by analyzing respective air quality monitoring station data along with CG lightning and meteorological data. We observed NO x enhancement and significant O 3 decline on lightning days. Influences of land use types, lightning activities and meteorological conditions on surface NO x and O 3 were examined. NO x and O 3 concentrations shifted towards higher and lower levels, respectively, during lightning days especially in the dominant wind directions. Principal component analysis/absolute principal component scores (PCA/APCS) method and stepwise multiple linear regression (MLR) analysis were employed to examine the influence of thunderstorm related lightning and meteorological parameters on surface NO x and O 3 . Wind speed was supposed to be the most important meteorological parameter affecting the concentration of NO x , and lightning activities were observed to make a positive contribution to NO x . Negative contribution of hot, cloudy and wet weather and positive contribution of wind speed were found to affect the concentration of O 3 . Lightning parameters were also found to make a small positive contribution to O 3 concentration at Tap Mun and Tung Chung, but the net effect of lightning activities and corresponding meteorological conditions was the decrease of O 3 on lightning days. Reasonably good agreement between the predicted and observed NO x and O 3 values indicates that PCA/APCS-MLR is a valuable method to study the thunderstorm induced NO x and O 3 variations. [ABSTRACT FROM AUTHOR]

Cloud-to-ground (CG) lightning activity recorded by the Hellenic National Meteorological Service (HNMS) Precision Lightning Network (PLN) is analysed over the wider area of Greece. In addition, the spatial and temporal relationships between TRMM 3B42 (Tropical Rainfall Measuring Mission) datasets and lightning are presented. The analyses concern the period from January 14, 2008 to December 31, 2012. The Laboratory of Climatology and Atmospheric Environment, University of Athens, has established a detailed dataset of lightning impacts over Greece from 1895 to 2013, based on digitized archive editions of newspapers. The mean seasonal variability of CG lightning activity revealed autumn as the most dominant season with 303 LD, while the mean monthly variability of CG indicated October as the most lightning active month and May as the month with a mean of 27 LD. The mean annual spatial distribution of CG lightning per km 2 , depicted the maximum frequency over Pindus mountain range (> 7 CG/km 2 ). During the autumn season, the northern Ionian Sea experienced a mean frequency of more than 5 CG/km 2 , compared to the southern Ionian Sea and NW Peloponnesus, where values of more than 7 CG/km 2 are depicted. During the summer season, the maximum frequency appeared along Pindus mountain range, around Attica, Thessaly and central Macedonia highlands. The spatial distribution of seasonal correlations between the number of CG flashes/day and gridded (TRMM 3B42) daily rainfall totals for the period 2008–2012 over Greece, indicated that correlations were mainly positive all over the under study area, within all seasons, and especially during summer and autumn. Regarding the lightning impacts in Greece, based on the 1895–2013 study period, more than 343 fatalities and at least 224 injured people have been recorded. The spatial analysis of lightning impacts, showed that the majority of events has been recorded over Greek mainland and only few scattered events have been reported over Ionian and Aegean Seas. The results of the performed research for Greece, during 1895–2013 (2000–2013), indicated that fatalities/injuries caused by lightning, were estimated at 2.9 (2) deaths/1.9 (1.6) injuries per year, respectively. [ABSTRACT FROM AUTHOR]

Research presents an overview on thunderstorm occurrence in Poland and focuses mainly on the relationship between human observations of thunderstorms (SYNOP daily summaries) and instrumental lightning detection data (PERUN network) in the timeframe between 2002 and 2013. The total of 4,952,203 cloud-to-ground flashes (2082 days with thunderstorms) derived from the PERUN lightning database, and 12,419 daily thunderstorm SYNOP reports from 44 meteorological stations (1417 days with thunderstorms) are compared. Within the use of two different computational methods, we define the threshold value of the human average observational thunderstorm detection range within a meteorological station. Results indicate that the average of this value ranges from 16.9 km (Delta computational method) to 18.3 km (threat score computational method). Given the limitations of both methods, we believe that the average of these two (17.5 km) may be the most reliable estimate that expresses how lightning is perceived by humans. Large differences in observational range values between some of the stations (e.g. from 12 km in Bielsko-Biała to 24 km in Łeba) indicate that thunderstorm measurements performed by humans are not homogeneous and are prone to errors. We estimate that an average increase/decrease of observational range by approximately 1 km results in 1 additional/redundant day in the average annual number of thunderstorm days in the climatological sense. Results indicate that already existing thunderstorm climatology papers that are based on SYNOP thunderstorm reports may present presumably not entirely reliable results and overestimate or underestimate values from the real distribution. [ABSTRACT FROM AUTHOR]

Abstract: Lightning is a natural phenomenon in the atmosphere, being a major cause of storm related deaths, main trigger of forest fires and affects many electrochemical systems of the body. Significant scientific interest has come up in the last decades, as numerous lightning detection networks have been established in operational basis, providing lightning data to assess and mitigate lightning impact to the local society by spatio-temporal analysis. In this study, a preliminary analysis of spatial and temporal variabilities of recorded lightnings over Greece during the period from January 2008 to December 2009 is presented. The data for retrieving the location and time-of-occurrence (TOA) of lightning were acquired from the Hellenic National Meteorological Service (HNMS). An operational precision lightning network (PLN) has been established since 2007 by HNMS, consisting of eight time-of-arrival (TOA) sensors, spatially distributed across Greek territory. The spatial variability of lightnings revealed their incidence within specific geographical sub-regions while the temporal variability concerns the seasonal and monthly distributions. All the analyses were carried out with respect to cloud to cloud (CC), cloud to ground (CG) and ground to cloud (GC) lightnings, within the examined time period. During the autumn season, lightning activity was the highest, followed by summer and spring. Higher frequencies of stokes appear over Ionian Sea and Aegean Sea than over land during winter period against continental mountainous regions during summer period. [Copyright &y& Elsevier]

Abstract: This paper presents the spatial and temporal distribution of cloud-to-ground lightning over Estonia and the adjacent sea for the period 2005–2009. Data collected by the NORDLIS (NORDic Lightning Information System) lightning detection network was used. The spatial distribution of lightning was calculated in a 10×10km grid. A total of 172,613 cloud-to-ground flashes were registered in the area under observation during 2005–2009. The annual mean cloud-to-ground flash density over the area was 0.34 flashes km−2 year−1. The lowest values found were less than 0.10 flashes km−2 year−1 and the highest flash densities were 0.80–1.01 flashes km−2 year−1. The monthly distribution of lightning showed the highest activity in July and August. Of all the registered flashes, 99.4% were reported from May to October. The daily distribution of flashes showed single days on which thunderstorm activity was very high, against a background of much lower everyday activity. The diurnal distribution of lightning showed an evident peak between 15:00 and 17:00 local time over land. Over the sea, a flatter maximum lay between 13:00 and 21:00. Minimum lightning activity occurred between 22:00 and 06:00 over land and from 02:00 to 09:00 over the sea. Our work revealed that the spatial and temporal characteristics of cloud-to-ground lightning over Estonia generally resemble the characteristics found at other mid-latitude study sites. [Copyright &y& Elsevier]

Abstract: A long term (1998–2006) study of annual precipitation and cloud-to-ground (CG) lightning has been made at 31 stations over Taiwan. The CG-lightning data were collected by the ground-based Lightning Location System (LLS) built by Tai-Power Company of Taiwan while the precipitation data were collected from the Central Weather Bureau (CWB) of Taiwan. For the present study, a spatial scale of 0.1° latitude×0.1° longitude (≈102 km2) is selected to determine the flash density. CG-lightning and precipitation data are used to compute the values of “rain yield”, defined as the mass of rain produced per CG-lightning flash in units of kgfl−1 over a given surface area. The rain yield is found to vary considerably with seasonal and climatic conditions, and geographical location. A positive linear correlation is observed between precipitation and lightning flash density with a highest correlation coefficient of 0.70 over inland stations. Out of the 31 stations, 13 stations are inland stations and these stations show higher rain yields clustering close to a mean of 0.7×1010 kgfl−1, compared to the coastal stations which show a mean value 1.4×1010 kgfl−1. When the stations are classified according to seasonal climate zones, the winter and winter-dominant rainfall stations show comparatively higher value of rain yield with an average of 2.8×1010 kgfl−1 than the summer and summer-dominant rainfall stations which exhibit a significantly lower value of rain yield of 2.1×1010 kgfl−1. Inland stations exhibit a lower value of rain yield with a mean of 1.6×109 kgfl−1 and 1.4×1010 kgfl−1 respectively during warm and cold seasons compared to the coastal stations. For each station, the average cold season rain yields are significantly higher than that of warm season values. These differences in rain yield values are attributed to local surface heating which indirectly controls such parameters as cloud base height and convectively available potential energy (CAPE) in the atmosphere. The variation of rain yield with geographical, seasonal, and climatic conditions, found in our observations, are in good agreement with studies found in the literature from other parts of the world. [Copyright &y& Elsevier]

Abstract: 2-D 12.5 m-resolution simulations of cloud-to-ground (CG) lightning discharge processes have been performed using an improved stochastic lightning model for different types of cloud charge distributions, such as dipole, tripole, bi-dipole and multi-layer charge structures produced from the numerical simulation of thundercloud electrification. The modelling produced the fine branched channel structure of CG lightning and the results illustrate the relations between CG lightning channel propagation and cloud charge distribution. The simulated features of CG lightning are associated with the observed results. The simulation studies are essential in our understanding of complex charge transfer processes caused by CG lightning discharges in thunderclouds. The induced charges of opposite polarity are deposited or embedded in the local volumes where the bidirectional leaders passed during a CG lightning discharge. Although the embedding affects charge structure only in a pair of significant positive and negative charge regions closest to the ground, the electric field strength acutely weakens and electrostatic energy in thunderclouds is significantly consumed when the discharge terminates. In addition to simulating the upward and downward breakdown of the initial leader to ground and the ensuing return stroke (RS), the simulation assumes that current continues to flow in the channel to ground and determines the upward breakdown until the end of the discharge. For the subsequent discharge sub-process, the upward leader channel tends to transfer the charges with the same polarity as the RS, while the downward leader channel favors transfer of opposite charge to ground. In the sub-processes of a few CG flash simulations, the magnitude of the opposite charges from the downward leader exceeds that of charges with the same polarity from the upward leader so that the net charges transferred to the ground have a reversed polarity to the RS. The simulation presents similar features of CG lightning as those observed in realistic bipolar CG lightning. [Copyright &y& Elsevier]

Abstract: The observed reduction in cloud-to-ground lightning in the near-equatorial zone is examined from the perspective of the width of the main negative charge region. Thermodynamic observations of cloud base height also show a climatological minimum value in the near-equatorial region. The association of low cloud bases with both narrow updrafts and narrow charging zones may impede the bridging of the large air gap to ground, and thereby suppress cloud-to-ground lightning activity. This width dependence may be more important than the ∼10% variation in height of the freezing level in encouraging flashes to ground. [Copyright &y& Elsevier]

Abstract: Concentrations of both nitrogen oxides (NO x =NO+NO2) observed at a station at high altitude (Puy de Dome (PDD), 1465 m) have been analyzed in relation with the cloud-to-ground (CG) lightning activity provided by the detection network Météorage. A first analysis of the time series of both types of data issued for 4 months of the 2003 summer shows a good correspondence between high values of NO x and stormy conditions in the area. During this 4-month period, NO x values exceeding 100 μg m−3 have been observed on 7 days and all of these days correspond to lightning activity in a 200×200 km2 area around PDD. Thirty-three days of the period experience lightning activity in this area, and only 14 of these days (42%) correspond to NO x peak values exceeding 50 μg m−3. The presence of lightning activity is a necessary condition to have very large peak values of NO x at PDD, but this condition is not sufficient. Two days showed NO x exceeding 300 μg m−3 which represents a value between 176 and 270 ppbv according to the respective proportion of NO2 and NO. Six days are analyzed in detail, using other information about the convective system and the wind conditions. The data of urban stations close to PDD have also been considered in the analysis for evaluating the possible transport by a plume from a city area. These days include the higher NO x cases, cases with high lightning activity, and cases with remote lightning activity. On each of these days, the location of the CG flashes, the time delays between lightning activity and NO x increase, and the air flow seem consistent with an interpretation of NO x produced by lightning. The higher values of NO x correspond with close and stationary thunderstorms which produced large proportions of positive CG flashes with low wind conditions. However, the characteristic increase seems to depend on several parameters of the CG flashes: their rate, location, and polarity. By comparing with the values given by other authors for aircraft measurements at altitude, our observations indicate that large quantities of NO x could be produced by the CG flash processes. [Copyright &y& Elsevier]

The monthly convective precipitation (CP) and convective precipitation rate (CPR) over the western Mediterranean Sea are estimated using cloud-to-ground lightning flashes for the June to October period using data of 3 years (1992–1994). Rain yield was computed using the precipitation data from seven observing stations (all equipped with rain gauges) located on the Mediterranean coast of the Iberian Peninsula and in the Balearic Islands. The values obtained were 0.93×108 kg/fl for the negative flashes and 20.63×108 kg/fl for the positive flashes. Convective precipitation over sea was estimated from the rain yield using the cloud-to-ground (CG) lightning activity detected by a lightning detection network. Because no measured data on precipitation over sea are available, the estimated convective precipitation was compared with the monthly diagnostic surface convective precipitation data from the NOAA NCEP/NCAR climate data assimilation system. Analysis of the results revealed that convective precipitation over the western Mediterranean Sea is maximum in the months September and October and near the northeastern coast of the Iberian Peninsula (maximum in the order of 240 mm/month). The convective precipitation rate exhibits less time variability than convective precipitation, although its spatial distribution is similar. [Copyright &y& Elsevier]

The average monthly, seasonal and annual lightning event duration and lightning flash rates over the Iberian Peninsula were estimated using cloud-to-ground lightning flashes for the 1992–1994 period. The total lightning event duration was over 37,000 h year−1. Maximum values were found during the summer and were seen to be associated with mountainous areas, while minimum values were found during the winter and in the western and southern parts of the Iberian Peninsula. The spatial pattern of lightning event duration exhibited significant seasonal variations. The annual average of the mean and peak lightning flash rate was found to be 8.7 and 78.3 flashes (fl) h−1, respectively. The temporal and spatial variations in flash rate were similar to those of lightning event duration, but with significant differences. In general, lightning flash rate exhibited fewer temporal and spatial variations than lightning event duration. [Copyright &y& Elsevier]

Lightning is one of the most dangerous natural phenomena, able to produce high impacts and damage on human beings and infrastructures (civil, electric, telecommunications, etc..) even though perception of it as a hazard is low. The aim of this study is to provide a detailed analysis of lightning occurrence throughout the Italian territory to support the work of different operators and researchers (physicists, meteorologists and electric/ITC engineers) improving knowledge about the main properties of lightning. Thus, an in-depth study of the statistics of lightning activity across the Italian territory for the period 2010–2019 is performed in detail using the data collected by the Italian Lightning Detection Network SIRF (Sistema Italiano Rilevamento Fulmini), part of the European network EUCLID (European Cooperation for Lightning Detection). This analysis presents general properties such as Ground Stroke Density (GSD) and the positive to negative strokes ratio by highlighting how seasonal, geographical and orographic factors influence their values. Then, attention is focused on lightning peak current, on flash multiplicity and on the distance between the points of impact of different strokes within a flash. Comparison made with other articles available in the literature reveals good agreement with studies conducted with other LLS data in Mediterranean regions. On the other hand, some differences appear with direct current measurements that can be partly ascribed to Lightning Location System (LLS) detection contamination (confirming other comparative studies of LLS and instrumented tower findings), to differences between tower and ground measures, and to the presence of regional differences. • Inter-annual variability: highest GSD between June and August over the land and between August and October above the sea. • Monthly negative/positive CG flashes ratio is always in the range around 4÷14. • Highest concentration of flashes: between 10 UTC and 17 UTC (over the land) and constant along the day (above the sea). • In the northern part of Italy, positive and negative strokes are characterized by a more evident seasonal variability. • Highest current peak values are observed during periods of lowest lightning activity. [ABSTRACT FROM AUTHOR]

The results of observations of radio emission from thunderclouds in a wide frequency range with a high temporal resolution carried out in the Upper Volga region near Nizhny Novgorod are compared with the data from worldwide and regional lightning location networks. Two parameters are chosen to characterize the radio emission: root mean square (corresponding to the emission intensity) and kurtosis (to testify to the presence of a pulsed component in the emission) of its distributions at short time intervals. It is shown that the intensity of radio emission as a whole reflects the level of thunderstorm activity at distances up to 50 km from the point of observation. A similar correlation also takes place for the kurtosis of the emission. Comparison with events detected by lightning location networks shows that they are often preceded by a well-defined behavior of the above parameters. The emission begins suddenly with a moderate level of intensity and a high value of kurtosis that lasts from few to more than one hundred of milliseconds. Then the kurtosis decreases permanently with approximately the same intensity of the emission that can correspond to a step leader stage of a lightning discharge. The radio frequency event is ended by a sharp increase in the emission intensity simultaneously with a decrease of the kurtosis to the background level, and exactly the same moment corresponds to a lightning location network event that can be associated with the return stroke of a lightning discharge. It should be mentioned that a number of events from lightning location networks have no such manifestations in the recorded radio emission and vice versa. • Wideband high frequency radio emission characterizes thunderstorm activity at moderate distances from a point of observation. • Cloud-to-ground lightning discharges can be identified by a well-defined thundercloud high frequency radio emission behavior. • Most lighning are registered simultaneously in high frequency radio emission and by lightning location networks. • A number of events registered by lightning location networks have no manifestations in high frequency and vice versa. [ABSTRACT FROM AUTHOR]