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Showing papers on "Thunderstorm published in 2019"


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the climatology of (severe) thunderstorm days on a pan-European scale for the period of 1979-2017, using sounding measurements, surface observations, and lightning data.
Abstract: The climatology of (severe) thunderstorm days is investigated on a pan-European scale for the period of 1979–2017. For this purpose, sounding measurements, surface observations, lightning d...

83 citations


Journal ArticleDOI
TL;DR: The results show that the deep learning algorithm had a higher classification accuracy on HR and hail than support vector machine, random forests, and other traditional machine learning algorithms and showed better forecasting skills than the subjective forecasts by the forecasters.
Abstract: A deep learning objective forecasting solution for severe convective weather (SCW) including short-duration heavy rain (HR), hail, convective gusts (CG), and thunderstorms based on numerical weather prediction (NWP) data was developed. We first established the training datasets as follows. Five years of severe weather observations were utilized to label the NCEP final (FNL) analysis data. A large number of labeled samples for each type of weather were then selected for model training. The local temperature, pressure, humidity, and winds from 1000 to 200 hPa, as well as dozens of convective physical parameters, were taken as predictors in our model. A six-layer convolutional neural network (CNN) model was then built and trained to obtain optimal model weights. After that, the trained model was used to predict SCW based on the Global Forecast System (GFS) forecast data as input. The performances of the CNN model and other traditional methods were compared. The results show that the deep learning algorithm had a higher classification accuracy on HR and hail than support vector machine, random forests, and other traditional machine learning algorithms. The objective forecasts by use of the deep learning algorithm also showed better forecasting skills than the subjective forecasts by the forecasters. The threat scores (TSs) of thunderstorm, HR, hail, and CG were increased by 16.1%, 33.2%, 178%, and 55.7%, respectively. The deep learning forecast model is currently used in the National Meteorological Center of China to provide guidance for the operational SCW forecasting over China.

64 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported the simultaneous detection of a gamma-ray glow and a downward terrestrial gamma ray flash suggesting the origin of the two phenomena are related, and suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF.
Abstract: Two types of high-energy events have been detected from thunderstorms. One is “terrestrial gamma-ray flashes” (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting “gamma-ray glows”. Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for ~100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within ~1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF. Thunderstorms are thought to produce two types of high-energy emissions, terrestrial gamma-ray flashes and gamma-ray glows however due to the difficulty in their observation the exact relation between the two is still not well-understood. Here, the authors report the simultaneous detection of a gamma-ray glow and a downward terrestrial gamma-ray flash suggesting the origin of the two phenomena are related.

62 citations


Journal ArticleDOI
08 Nov 2019
TL;DR: In this paper, a four-parameter model based on four commonly available surface weather variables (air pressure at station level (QFE), air temperature, relative humidity, and wind speed) was developed for hindcast nearby and distant lightning hazards by looking at single site observations of meteorological parameters.
Abstract: Lightning discharges in the atmosphere owe their existence to the combination of complex dynamic and microphysical processes. Knowledge discovery and data mining methods can be used for seeking characteristics of data and their teleconnections in complex data clusters. We have used machine learning techniques to successfully hindcast nearby and distant lightning hazards by looking at single-site observations of meteorological parameters. We developed a four-parameter model based on four commonly available surface weather variables (air pressure at station level (QFE), air temperature, relative humidity, and wind speed). The produced warnings are validated using the data from lightning location systems. Evaluation results show that the model has statistically considerable predictive skill for lead times up to 30 min. Furthermore, the importance of the input parameters fits with the broad physical understanding of surface processes driving thunderstorms (e.g., the surface temperature and the relative humidity will be important factors for the instability and moisture availability of the thunderstorm environment). The model also improves upon three competitive baselines for generating lightning warnings: (i) a simple but objective baseline forecast, based on the persistence method, (ii) the widely-used method based on a threshold of the vertical electrostatic field magnitude at ground level, and, finally (iii) a scheme based on CAPE threshold. Apart from discussing the prediction skill of the model, data mining techniques are also used to compare the patterns of data distribution, both spatially and temporally among the stations. The results encourage further analysis on how mining techniques could contribute to further our understanding of lightning dependencies on atmospheric parameters.

61 citations


Journal ArticleDOI
TL;DR: In this article, two typical wind events including the thunderstorm wind and thermally developed wind are highlighted, and an automatic classification method is proposed to extract and separate these wind events, to capture the rapid variation of its maximum wind speed, mean temperature and mean humidity through the boxplot method.

60 citations


Journal ArticleDOI
TL;DR: The value that the development of a reprocessed GLM science product would offer and how such a product might be created at a reduced computational cost are demonstrated are demonstrated.
Abstract: The Lightning Cluster Filter Algorithm in the Geostationary Lightning Mapper (GLM) ground system identifies lightning flashes from the stream of event detections. It excels at clustering simple flashes but experiences anomalies with complex flashes that last longer than 3 s or contain more than 100 groups, leading to flashes being artificially split. We develop a technique that corrects these anomalies and apply it to the 2018 GLM data to document all lightning across the Americas. We produce statistics describing the characteristics and frequencies of reclustered GLM flashes and thunderstorm area features. The average GLM Americas flash rate in 2018 was 11.7 flashes per second with the greatest flash rate densities occurring over Lake Maracaibo (157 flashes per km2/year). Lloro, Choco, Colombia had the most thunderstorm activity with 256 thunder days. The longest GLM flash spanned 673 km, the largest flash covered 114,997 km2, and the longest-lasting flash had a 13.496-s duration. The first case occurred over Rio Grande do Sul in Brazil, while the other two cases occurred in the central United States. All three extreme flashes are located in the stratiform regions of Mesoscale Convective Systems. The highest flash rate for a thunderstorm area feature was 17.6 flashes per second, while the largest thunderstorm was 216,865 km2 in size. Both storms occurred in South America. These initial results demonstrate the value that the development of a reprocessed GLM science product would offer and how such a product might be created at a reduced computational cost.

55 citations


Journal ArticleDOI
27 Aug 2019
TL;DR: Radler et al. as mentioned in this paper applied a set of additive regression models to an ensemble of 14 regional climate simulations and found that convective instability will increase as a result of rising humidity near the earth's surface.
Abstract: We show that the frequency of damaging convective weather events including lightning, hail and severe wind gusts will likely increase over Europe until the end of this century. We apply a set of additive regression models to an ensemble of 14 regional climate simulations and find that convective instability will increase as a result of rising humidity near the earth’s surface. Even though a slight decrease in thunderstorm occurrence in southwestern and southeastern Europe is projected, the probability of severe weather will increase throughout Europe, in particular for very large hail. It might be expected that Arctic amplification would lead to a weaker jet stream and, thus lower vertical wind shear, but we find instead that the jet changes little or even increases in situations with convective instability. To cope with the rising hazard probabilities, risk models will need to be adapted, while investment in sturdier structures, like the use of hardened glass in greenhouses or solar panels, will become more cost-effective. Furthermore, the need will grow to advise the public on loss prevention by taking precautionary measures as storms approach. Damaging weather events such as lightning, hail, and severe wind gusts are likely to become more common across Europe over the next several decades. Increased global temperatures, high low-level humidity levels and a changing polar jet stream are all associated with anthropogenic climate change; however, the implications of such projected changes in relation to severe weather events are still being explored. Here, Anja Radler and colleagues use numerical simulations of regional climate to predict the severity and frequency of convective storms in Europe under projected anthropogenic climate conditions. They find that the probability of severe weather and thunderstorms are expected to increase throughout Europe, and in particular, very large hail is likely to become more common. Therefore, public warnings and precautionary measures and should be actioned as storms approach.

52 citations


Journal ArticleDOI
TL;DR: In this article, the authors document atmospheric conditions, development, and evolution of a severe weather outbreak that occurred on 11 August 2017 in Poland, focusing on analyzing system morphologies and their evolution.
Abstract: This study documents atmospheric conditions, development, and evolution of a severe weather outbreak that occurred on 11 August 2017 in Poland. The emphasis is on analyzing system morpholog...

49 citations


Journal ArticleDOI
TL;DR: The data fusion of multiple sources, coupled with the machine learning approach, makes it possible to greatly improve the robustness of large hail prediction compared to any single product commonly used in operational forecasting.

39 citations


Journal ArticleDOI
TL;DR: It is demonstrated that machine learning can skillfully classify thunderstorms into three categories: supercell, part of a quasi-linear convective system, or disorganized.
Abstract: We demonstrate that machine learning (ML) can skillfully classify thunderstorms into three categories: supercell, part of a quasi-linear convective system, or disorganized. These classifica...

37 citations


Journal ArticleDOI
06 Dec 2019
TL;DR: In this paper, the authors used two environmental parameters, the Large Hail Parameter and the Significant Hail Parameters, to assess trends in days with environments conducive for hail ≥ 5 cm.
Abstract: Understanding trends in large hail-producing environments is an important component of estimating hail risk. Here, we use two environmental parameters, the Large Hail Parameter and the Significant Hail Parameter, to assess trends in days with environments conducive for hail ≥5 cm. From 1979 to 2017, there has been an increase in days with favorable large hail environments in central and eastern portions of the U.S. This increase has been driven primarily by an increasing frequency of days with steep mid-tropospheric lapse rates and necessary combinations of instability and vertical wind shear for severe thunderstorms. Annual large hail environment area is significantly, positively correlated with (1) large hail report area east of the Rocky Mountains, and (2) large hail radar-derived area in the Midwest and Northeast. This evidence suggests that there may be an environmental fingerprint on increasing large hail risk and expanding this risk eastward.

Journal ArticleDOI
TL;DR: The history of severe thunderstorm research and forecasting over the past century has been a remarkable story involving interactions between technological development of observational and observational and forecasting tools as mentioned in this paper, which has been described in detail in a recent paper.
Abstract: sThe history of severe thunderstorm research and forecasting over the past century has been a remarkable story involving interactions between technological development of observational and ...

Journal ArticleDOI
TL;DR: In this article, a novel directional decomposition strategy is formulated, which makes the study of thunderstorm outflows and synoptic winds fully coherent, and the results provided by the classic and novel decomposition rules are first compared and elucidated with reference to a couple of real thunderstorm and Synoptic wind velocity records.

Journal ArticleDOI
TL;DR: This work uses data from a satellite-based product, Rapidly Developing Thunderstorms, to estimate a model of the uncertain evolution of thunderstorms, and introduces a methodology based on numerical optimal control to generate avoidance trajectories under uncertain convective weather evolution.

Journal ArticleDOI
TL;DR: The southeastern United States has become a prime area of focus in tornado-related literature due, in part, to the abundance of tornadoes occurring in high-shear low-CAPE (HSLC) environment.
Abstract: The southeastern United States has become a prime area of focus in tornado-related literature due, in part, to the abundance of tornadoes occurring in high-shear low-CAPE (HSLC) environment...

Journal ArticleDOI
TL;DR: This study is the first to demonstrate how a computationally feasible increase of model resolution over West Africa – allowing to avoid convection parameterisation – yields a better representation of organised convection in the Sahel and of moisture within the monsoon system, ultimately improving 5–8-day tropical and mid-latitude weather forecasts.
Abstract: The summertime West African Sahel has the worldwide highest degree of thunderstorm organisation into long-lived, several hundred-kilometre elongated, fast propagating systems that contribute 90% to the annual rainfall. All current global weather prediction and climate models represent thunderstorms using simplified parameterisation schemes which deteriorates the modelled distribution of rainfall from individual storms and the entire West African monsoon circulation. It is unclear how this misrepresentation of Sahelian convection affects forecasts globally. Our study is the first to demonstrate how a computationally feasible increase of model resolution over West Africa - allowing to avoid convection parameterisation - yields a better representation of organised convection in the Sahel and of moisture within the monsoon system, ultimately improving 5-8-day tropical and mid-latitude weather forecasts. We advocate an operational use of a modelling strategy similar to the one presented here for a cost-effective improvement of global weather prediction and potentially even (sub-)seasonal and climate simulations.

Journal ArticleDOI
TL;DR: In this article, the authors used radar network and lightning mapping array observations over Alabama of a large and diverse sample of 33 storms are input to hydrometeor identification, vertical velocity retrieval and flash rate algorithms to develop and test flash rate relations.
Abstract: Lightning flash rate parameterizations based on polarimetric and multi-Doppler radar inferred microphysical (e.g., graupel volume, graupel mass, 35 dBZ volume) and kinematic (e.g., updraft volume, maximum updraft velocity) parameters have important applications in atmospheric science. Although past studies have established relations between flash rate and storm parameters, their expected performance in a variety of storm and flash rate conditions is uncertain due to sample limitations. Radar network and lightning mapping array observations over Alabama of a large and diverse sample of 33 storms are input to hydrometeor identification, vertical velocity retrieval and flash rate algorithms to develop and test flash rate relations. When applied to this sample, prior flash rate linear relations result in larger errors overall, including often much larger bias (both over- and under-estimation) and root mean square errors compared to the new linear relations. At low flash rates, the new flash rate relations based on kinematic parameters have larger errors compared to those based on microphysical ones. Sensitivity of error to the functional form (e.g., zero or non-zero intercept) is also tested. When considering all factors (e.g., low errors including at low flash rate, consistency with past linear relations, and insensitivity to functional form), the flash rate parameterization based on graupel volume has the best overall performance.


Journal ArticleDOI
TL;DR: In this article, the ability of Atmospheric Emitted Radiance Interferometer (AERI) and Doppler lidar (DL) wind profile observations to impact short-term forecasts of convection is explored by assimilating r...
Abstract: The ability of Atmospheric Emitted Radiance Interferometer (AERI) and Doppler lidar (DL) wind profile observations to impact short-term forecasts of convection is explored by assimilating r...

Journal ArticleDOI
TL;DR: The authors used the NOAA Air Resources Laboratory (ARL) to demarcate the source regions of low-level moisture for the source of severe thunderstorms, but the demarcation was not explicitly demarcated.
Abstract: Tornadic thunderstorms rely on the availability of sufficient low-level moisture, but the source regions of that moisture have not been explicitly demarcated. Using the NOAA Air Resources L...

Journal ArticleDOI
TL;DR: In this paper, the potential value of a radar-driven field campaign to constrain simulation of isolated convection subject to a strong aerosol perturbation, convective cells observed by the operational KHGX weather radar in the vicinity of Houston, Texas, are examined individually and statistically.
Abstract: . To probe the potential value of a radar-driven field campaign to constrain simulation of isolated convection subject to a strong aerosol perturbation, convective cells observed by the operational KHGX weather radar in the vicinity of Houston, Texas, are examined individually and statistically. Cells observed in a single case study of onshore flow conditions during July 2013 are first examined and compared with cells in a regional model simulation. Observed and simulated cells are objectively identified and tracked from observed or calculated positive specific differential phase ( KDP ) above the melting level, which is related to the presence of supercooled liquid water. Several observed and simulated cells are subjectively selected for further examination. Below the melting level, we compare sequential cross sections of retrieved and simulated raindrop size distribution parameters. Above the melting level, we examine time series of KDP and radar differential reflectivity ( ZDR ) statistics from observations and calculated from simulated supercooled rain properties, alongside simulated vertical wind and supercooled rain mixing ratio statistics. Results indicate that the operational weather radar measurements offer multiple constraints on the properties of simulated convective cells, with substantial value added from derived KDP and retrieved rain properties. The value of collocated three-dimensional lightning mapping array measurements, which are relatively rare in the continental US, supports the choice of Houston as a suitable location for future field studies to improve the simulation and understanding of convective updraft physics. However, rapid evolution of cells between routine volume scans motivates consideration of adaptive scan strategies or radar imaging technologies to amend operational weather radar capabilities. A 3-year climatology of isolated cell tracks, prepared using a more efficient algorithm, yields additional relevant information. Isolated cells are found within the KHGX domain on roughly 40 % of days year-round, with greatest concentration in the northwest quadrant, but roughly 5-fold more cells occur during June through September. During this enhanced occurrence period, the cells initiate following a strong diurnal cycle that peaks in the early afternoon, typically follow a south-to-north flow, and dissipate within 1 h, consistent with the case study examples. Statistics indicate that ∼ 150 isolated cells initiate and dissipate within 70 km of the KHGX radar during the enhanced occurrence period annually, and roughly 10 times as many within 200 km, suitable for multi-instrument Lagrangian observation strategies. In addition to ancillary meteorological and aerosol measurements, robust vertical wind speed retrievals would add substantial value to a radar-driven field campaign.

Journal ArticleDOI
TL;DR: In this paper, the characteristics of a wide dataset of thunderstorm signals are analyzed in a statistical environment coherent with the traditional one for synoptic winds; in this stage of the research, estimations of the mean wind speed and direction, the turbulence parameters and gust factor are carried out considering the records as disjoint from each other.

Journal ArticleDOI
TL;DR: The first such images are reported, showing a step-wise evolution of gigantic jets during their rising phase, as magnetic field signals tracking the charge transfer and optical Geostationary Lightning Mapper data are matched unambiguously to the precisely timed final jump process in a gigantic jet.
Abstract: In 2002 it was discovered that a lightning discharge can rise out of the top of tropical thunderstorms and branch out spectacularly to the base of the ionosphere at 90 km altitude. Several dozens of such gigantic jets have been recorded or photographed since, but eluded capture by high-speed video cameras. Here we report on 4 gigantic jets recorded in Colombia at a temporal resolution of 200 µs to 1 ms. During the rising stage, one or more luminous steps are revealed at 32-40 km, before a continuous final jump of negative streamers to the ionosphere, starting in a bidirectional (bipolar) fashion. The subsequent trailing jet extends upward from the jump onset, with a current density well below that of lightning leaders. Magnetic field signals tracking the charge transfer and optical Geostationary Lightning Mapper data are now matched unambiguously to the precisely timed final jump process in a gigantic jet. Gigantic jets, lightning discharges originating from tropical thunderstorms that can reach the base of the ionosphere at 90 km altitude, have not been captured using high-speed video cameras before. Here, the first such images are reported, showing a step-wise evolution of gigantic jets during their rising phase.

Journal ArticleDOI
TL;DR: Analysis of the probability of detection and the false alarm ratio scores showed the superiority of the F2 classification function, with the best performance in May, followed by June and September, which will be integrated into the Bulgarian Integrated NowCAsting tool for thunderstorm forecasting in the warm/convective season.
Abstract: Bulgaria is a country with a high frequency of hail and thunderstorms from May to September. For the May–September 2010–2015 period, statistical regression analysis was applied to identify predictors/classification functions that contribute skills to thunderstorm forecasting in the Sofia plain. The functions are based on (1) instability indices computed from radiosonde data from Sofia station F1, and (2) combination of instability indices and Integrated Water Vapor (IWV), derived from the Global Navigation Satellite System (GNSS) station Sofia-Plana, F2. Analysis of the probability of detection and the false alarm ratio scores showed the superiority of the F2 classification function, with the best performance in May, followed by June and September. F1 and F2 scores were computed for independent data samples in the period 2017–2018 and confirmed the findings for the 2010–2015 period. Analysis of IWV and lightning flash rates for a multicell and supercell thunderstorm in June and July 2014 showed that the monthly IWV thresholds are reached 14.5 and 3.5 hours before the thunderstorm, respectively. The supercell IWV peak registered 40 min before the thunderstorm, followed by a local IWV minimum corresponding to a peak in the flash rate. In both cases, an increase of IWV during severe hail was registered, which is likely related to the hydrometeor contribution to GNSS path delay. The results of this study will be integrated into the Bulgarian Integrated NowCAsting tool for thunderstorm forecasting in the warm/convective season.

Journal ArticleDOI
TL;DR: In this article, a statistically significant link between atmospheric blocking located over the eastern North Atlantic and northern Europe and warm season thunderstorm activity over western and central Europe was established through odds ratio analysis.
Abstract: A statistically significant link is presented between atmospheric blocking located over the eastern North Atlantic and northern Europe and warm‐season thunderstorm activity over western and central Europe. Lightning data from 2001 to 2014 were used to identify thunderstorm days and blocking events were extracted from the ERA‐Interim reanalysis using an objective identification algorithm. The statistical link between the two phenomena is established through odds ratio analysis. Two areas – one over the eastern part of the North Atlantic and one over the Baltic Sea – were identified as locations where blocking influences the occurrence of deep moist convection in parts of western and central Europe. Based on the mean ambient conditions on days with blocking in these two areas, well‐known dynamic and thermodynamic mechanisms supporting or suppressing the development of thunderstorms were confirmed. The anticyclonic circulation of a block over the eastern part of the North Atlantic leads to a northerly to northwesterly advection of dry and stable air masses into Europe on the eastern flank of the block. In addition, these environmental conditions are on average associated with large‐scale subsidence of air masses (convection‐inhibiting conditions). In contrast, the southerly to southwesterly advection of warm, moist and unstable air masses on the western flank of a block over the Baltic Sea results in convection‐favouring conditions over western and central Europe. Both blocking situations are on average associated with weak wind speeds at mid‐tropospheric levels and with weak wind shear. As a consequence, thunderstorms related to atmospheric blocking over the Baltic Sea tend to be on average less organised.

Journal ArticleDOI
TL;DR: In this paper, a new lightning data assimilation (LDA) scheme comprehensively nudging water contents in the WRF model is developed at cloud-resolving scale, which takes the dynamical and thermodynamic conditions into consideration and nudges the low-level water vapor and graupel mass within the mixed-phase region according to the detected total lightning flash rate and model environments.

Journal ArticleDOI
TL;DR: In this paper, the authors reviewed the scientific advances made in the field of atmospheric electricity in China from 2011 to 2018, covering the following five aspects: (1) lightning detection and location techniques; (2) discharge processes and parameters associated with rocket-triggered lightning; (3) physical processes in natural lightning and attachment to the ground; (4) lightning activities and charge structure in different thunderstorms; and (5) effects of thunderstorms on the upper atmosphere.
Abstract: Atmospheric electricity research has been conducted actively in China, having profited from the development and application of high temporal and spatial resolution lightning detection and location technologies. This paper reviews the scientific advances made in the field of atmospheric electricity in China from 2011 to 2018, covering the following five aspects: (1) lightning detection and location techniques; (2) discharge processes and parameters associated with rocket-triggered lightning; (3) physical processes in natural lightning and attachment to the ground; (4) lightning activities and charge structure in different thunderstorms; and (5) effects of thunderstorms on the upper atmosphere. In addition, some outstanding questions for future research are outlined.

Journal ArticleDOI
TL;DR: In this article, the authors used a Lightning Mapping Array (LMA) installed in northern Colombia, the charge structure, lightning leader initiations and the cloud-to-ground strokes rates of two thunderstorms have been analyzed.
Abstract: Charge structure derived from lightning leader development of tropical thunderstorms comprising equatorial latitudes of < ±10° has not been investigated yet. In this work, using a Lightning Mapping Array (LMA) installed in northern Colombia, the charge structure, lightning leader initiations and the cloud-to-ground strokes rates of two thunderstorms have been analyzed. Additionally, radar information is also included. The identification of the charge regions has been obtained by analyzing the propagation of lightning leader developments. Flashes initiate between 4 and 15 km altitude. High initiation rates are different in the two storms. In one case the high rates are found between 8 and 13 km. In the other these are found between 10 and 15 km. The storms show typical tripolar structure where the upper positive charge is present at 10 to ~15 km, the mid-level negative charge is found between 6 and 9 km and the lower positive charge between 4 and 6 km altitude. Intracloud lightning flashes with inverted polarity have been identified for short period. In other periods, screening layer flashes have been detected at 14-15 km. The overall results show that the charge structures in the two Colombian storms are similar to the ones reported in North-Central Florida, but with a significant difference being the more than 2 km higher initiation altitude in Colombia. The vertical configuration of the charge regions and the leader development of these thunderstorms might help to explain the occurrence of Terrestrial Gamma-ray Flashes in tropical thunderstorms

Journal ArticleDOI
TL;DR: In this paper, a 3D-based Foshan Total Lightning Location System (FTLLS) was installed and started its operation in the summer of 2013, which consists of nine sub-stations that receive electromagnetic waves associated with lightning discharges and locates VLF/LF (200 Hz-500 kHz) radiation sources in 3D.
Abstract: In the summer of 2013, a three-dimensional (3D)-based Foshan Total Lightning Location System (FTLLS), embedded with differential time of arrival (DTOA) techniques, was installed and started its operation in Foshan, Guangdong Province, China. In this paper, the geographical distribution and set-up information of FTLLS, the estimated locating errors and locating results, as well as its initial operation results are presented. FTLLS consists of nine sub-stations that receive electromagnetic waves associated with lightning discharges and locates VLF/LF (200 Hz–500 kHz) radiation sources in 3D. The remote sub-stations acquired triggered waveforms with a duration of 0.5 ms, a resolution of 12-bits, and a GPS-based sferic time tags of 24 h per day. Cloud-to-ground (CG) lightning events, intra-cloud (IC) lightning events and narrow bipolar events (NBEs) were located by FTLLS. Based on the Monte Carlo simulation, the two-dimensional horizontal location error is basically less than 100 m, and the vertical error (altitude) is less than 200 m when the lightning event occurs within the network. On the other hand, over 14 million lightning strikes were recorded successfully by FTLLS during the period of May to October in 2014, among which IC events, CG events and NBEs accounted for 65%, 34% and 1%, respectively. It is shown that FTLLS is capable of a fine three-dimensional (3D) location, in which the altitude parameters obtained are reasonable and well consistent with observed data in the previous studies. The location results of thunderstorms were additionally verified through simultaneously-observed radar data.

Journal ArticleDOI
TL;DR: The charge structure of the cloud system, as well as possible mechanisms that can produce the gamma ray glows, are explored, including an inverted charge structure, with an upper negative charge layer and a lower positive charge layer.
Abstract: In the spring of 2017 an ER-2 aircraft campaign was undertaken over continental United States to observe energetic radiation from thunderstorms and lightning. The payload consisted of a suite of instruments designed to detect optical signals, electric fields, and gamma rays from lightning. Starting from Georgia, USA, 16 flights were performed, for a total of about 70 flight hours at a cruise altitude of 20 km. Of these, 45 flight hours were over thunderstorm regions. An analysis of two gamma ray glow events that were observed over Colorado at 21:47 UT on 8 May 2017 is presented. We explore the charge structure of the cloud system, as well as possible mechanisms that can produce the gamma ray glows. The thundercloud system we passed during the gamma ray glow observation had strong convection in the core of the cloud system. Electric field measurements combined with radar and radio measurements suggest an inverted charge structure, with an upper negative charge layer and a lower positive charge layer. Based on modeling results, we were not able to unambiguously determine the production mechanism. Possible mechanisms are either an enhancement of cosmic background locally (above or below 20 km) by an electric field below the local threshold or an enhancement of the cosmic background inside the cloud but then with normal polarity and an electric field well above the Relativistic Runaway Electron Avalanche threshold.