Showing papers on "Lightning published in 2015"
TL;DR: The various methods to geolocate lightning, both ground-based and satellite-based, are summarized, and the characteristics of lightning data available from various sources are discussed.
Abstract: Ground-based and satellite-based lightning locating systems are the most common ways to detect and geolocate lightning. Depending upon the frequency range of operation, LLSs may report a variety of processes and characteristics associated with lightning flashes including channel formation, leader pulses, cloud-to-ground return strokes, M-components, ICC pulses, cloud lightning pulses, location, duration, peak current, peak radiated power and energy, and full spatial extent of channels. Lightning data from different types of LLSs often provide complementary information about thunderstorms. For all the applications of lightning data, it is critical to understand the information that is provided by various lightning locating systems in order to interpret it correctly and make the best use of it. In this study, we summarize the various methods to geolocate lightning, both ground-based and satellite-based, and discuss the characteristics of lightning data available from various sources. The performance characteristics of lightning locating systems are determined by their ability to geolocate lightning events accurately with high detection efficiency and with low false detections and report various features of lightning correctly. Different methods or a combination of methods may be used to validate the performance characteristics of different types of lightning locating systems. We examine these methods and their applicability in validating the performance characteristics of different LLS types.
146 citations
TL;DR: In this paper, the authors identified several TGF-associated lightning radio emissions in which the altitudes of in-cloud lightning leader pulses that precede and follow the TGF can be measured.
Abstract: Radio emissions continue to provide insight into the production of terrestrial gamma ray flashes (TGFs) by thunderstorms, including the critical question of the conditions under which they are generated. We have identified several TGF-associated lightning radio emissions in which the altitudes of in-cloud lightning leader pulses that precede and follow the TGF can be measured. We combine these with high absolute timing accuracy TGF observations from the Fermi satellite to determine the development of the lightning channel before, during, and after the TGF production. All of these TGFs were produced several milliseconds after the leader had initiated and when the leaders reached 1–2 km in length. After the TGFs, the leaders all continued to ascend for several more kilometers with no dramatic change in their characteristics, although they all exhibited high average velocities of 0.8–1.0 × 106 m/s. Implications in the context of TGF models are discussed. These results paint the first clear picture of the lightning processes that occur before, during, and after TGF production.
92 citations
TL;DR: In this article, a database consisting of approximately 4000 storm observations has been analyzed to determine environmental characteristics that produce high radar reflectivities above the freezing level, large total lightning flash rates on the order of 10 flashes per minute, and anomalous vertical charge structures (most notably, dominant midlevel positive charge).
Abstract: A database consisting of approximately 4000 storm observations has been objectively analyzed to determine environmental characteristics that produce high radar reflectivities above the freezing level, large total lightning flash rates on the order of 10 flashes per minute, and anomalous vertical charge structures (most notably, dominant midlevel positive charge). The storm database is drawn from four regions of the United States featuring distinct environments, each with coinciding Lightning Mapping Array (LMA) network data. LMAs are able to infer total lightning flash rates using flash clustering algorithms, such as the one implemented in this study. Results show that anomalous charge structures inferred from LMA data, significant lightning flash rates, and increased radar reflectivities above the freezing level tend to be associated with environments that have high cloud base heights (approximately 3 km above ground level) and large atmospheric instability, quantified by normalized convective available potential energy (NCAPE) near 0.2 m s−2. Additionally, we infer that aerosols may affect storm intensity. Maximum flash rates were observed in storms with attributed aerosol concentrations near 1000 cm−3, while total flash rates decrease when aerosol concentrations exceed 1500 cm−3, consistent with previous studies. However, this effect is more pronounced in regions where the NCAPE and cloud base height are low. The dearth of storms with estimated aerosol concentrations less than 700 cm−3 (approximately 1% of total sample) does not provide a complete depiction of aerosol invigoration.
85 citations
TL;DR: It is derived that lightning can start if the electric field is 15% of the breakdown field, and if elongated ice particles of 6 cm length and 100 free electrons per cm3 are present.
Abstract: We derive that lightning can start if the electric field is 15% of the breakdown field, and if elongated ice particles of 6 cm length and 100 free electrons per cm3 are present. This is one particular example set from a parameter range that we discuss as well. Our simulations include the permittivity e(ω) of ice. 100 free electrons per cm3 exist at 5.5 km altitude in air showers created by cosmic particles of at least 5×1015 eV. If the electric field zone is 3 m high and 0.2 km2 in the horizontal direction, at least one discharge per minute can be triggered. The size distribution of the ice particles is crucial for our argument; more detailed measurements would be desirable.
81 citations
TL;DR: In this paper, information on fatalities in India as a result of lightning flashes has been extracted from a database on disastrous weather events of the India Meteorological Department (IMD), records dating from 1979 to 2011 indicate that about 5259 persons have been killed by lightning strikes in India.
Abstract: Information on fatalities in India as a result of lightning flashes has been extracted from a database on disastrous weather events of the India Meteorological Department (IMD). Records dating from 1979 to 2011 indicate that about 5259 persons have been killed by lightning strikes in India. The maximum number of lightning fatalities was observed in the states of Maharashtra (29%), West Bengal (12%) and Uttar Pradesh (9%). The spatial variation shows that lightning fatalities are higher over west central India. A significant number of males (89%) have been killed by lightning flashes compared to females (5%) and children (6%) in India, which is most likely due to the larger proportion of males working and moving outdoors in lonely conditions. The overall fatality rate is about 0.25 per million population per year in India. The lightning fatalities are significantly more common in the rainy and the summer seasons. Comparisons were also made between the results of the present study and similar studies carried out in different parts of the world. Therefore, this study provides useful information on the risky lightning time in India to indicate a public awareness and lightning safety campaign.
77 citations
TL;DR: In this article, the authors investigated National Lightning Detection Network reports and lightning radio waveforms in a 44-day observation period to analyze the in-cloud (IC) events producing currents above 200 kA.
Abstract: We investigated National Lightning Detection Network reports and lightning radio waveforms in a 44 day observation period to analyze the in-cloud (IC) events producing currents above 200 kA. The results show that there are two distinct classes of IC lightning events with very high peak currents: the well-known narrow bipolar events, and a previously unreported type that we call energetic in-cloud pulses (EIPs). Their temporal and spatial context shows that EIPs are generated from existing negative polarity leaders that are propagating usually upward but sometimes downward. The nearly identical characteristics of EIPs and some previously reported terrestrial gamma ray flashes (TGFs) indicate a likely connection between the two, which further suggests the possibility of downward directed TGFs. These very high peak current IC events also suggest the association of EIPs with ionospheric perturbations and optical emissions known as elves.
72 citations
TL;DR: In this paper, a terrestrial gamma-ray flash (TGF) was observed at ground level at the Lightning Observatory in Gainesville, Florida, on June 13, 2014, with a duration of 16 μ s and consisted of 6 pulses, two of which exceeded the upper measurement limit of 5.7 MeV.
69 citations
TL;DR: It is demonstrated that glows are relatively a common phenomena near the tops of thunderstorms, when compared with events such as terrestrial gamma-ray flashes, which suggest the presence of relativistic runaway electron avalanches.
Abstract: Gamma-ray ‘glows’ are long duration (seconds to tens of minutes) X-ray and gamma-ray emission coming from thunderclouds. Measurements suggest the presence of relativistic runaway electron avalanches (RREA), the same process underlying terrestrial gamma-ray flashes. Here we demonstrate that glows are relatively a common phenomena near the tops of thunderstorms, when compared with events such as terrestrial gamma-ray flashes. Examining the strongest glow measured by the airborne detector for energetic emissions, we show that this glow is measured near the end of a downward RREA, consistent with occurring between the upper positive charge layer and the negative screening layer above it. The glow discharges the upper positive layer by ≥9.6 mA, strong enough to be an important charging mechanism of the storm. For this glow, the gamma-ray flux observed is close to the value at which relativistic feedback processes become important, with an avalanche multiplication factor of 4,500.
68 citations
TL;DR: In this paper, a detailed case study analysis of four thunderstorms was performed using polarimetric and multi-Doppler capabilities to provide specificity on the physical and dynamical drivers behind lightning jumps.
Abstract: A detailed case study analysis of four thunderstorms is performed using polarimetric and multi-Doppler capabilities to provide specificity on the physical and dynamical drivers behind lightning jumps. The main differences between small increases in the total flash rate and a lightning jump are the increases in graupel mass and updraft volumes ≥10 m s−1 between the −10° and −40°C isotherms. Updraft volumes ≥10 m s−1 increased in magnitude at least 3–5 min in advance of the increase in both graupel mass and total flash rate. Updraft volumes ≥10 m s−1 are more robustly correlated to total flash rate than maximum updraft speed over a thunderstorm’s entire life cycle. However, peak updraft speeds increase prior to 8 of the 12 lightning jumps examined. Decreases in mean and median flash footprint size during increases in total lightning are observed in all four thunderstorms and are most notable during development stages within the most intense storms. However, this inverse relationship breaks down on l...
65 citations
TL;DR: In this article, the simultaneous impacts of normalized convective available potential energy (NCAPE) and warm cloud depth (WCD) as well as cloud condensation nuclei concentrations (D ≥ 40nm; N40) on total lightning density (TLD), average height of 30 dBZ echoes (AVGHT30), and vertical profiles of radar reflectivity (VPRR) within individual convective features (CFs) observed by the Tropical Rainfall Measuring Mission satellite between 2004 and 2011 are analyzed to determine the relative roles of thermodynamics and aerosols as they modulate
Abstract: Convective features (CFs) observed by the Tropical Rainfall Measuring Mission satellite between 2004 and 2011 are analyzed to determine the relative roles of thermodynamics and aerosols as they modulate radar reflectivity and lightning. We studied the simultaneous impacts of normalized convective available potential energy (NCAPE) and warm cloud depth (WCD) as well as cloud condensation nuclei concentrations (D ≥ 40 nm; N40) on total lightning density (TLD), average height of 30 dBZ echoes (AVGHT30), and vertical profiles of radar reflectivity (VPRR) within individual CFs. The results show that TLD increases by up to 600% and AVGHT30 increases by up to 2–3 km with increasing NCAPE and N40 for fixed WCD. The partial sensitivities of TLD/AVGHT30 to NCAPE and N40 separately were comparable in magnitude but account for a fraction of the total range of variability (i.e., when the influences of NCAPE and N40 are considered simultaneously). Both TLD and AVGHT30 vary inversely with WCD such that maxima of TLD and AVGHT30 are found for the combination of high NCAPE, high N40, and shallower WCD. The relationship between lightning and radar reflectivity was shown to vary as a function of N40 for a fixed thermodynamic environment. Analysis of VPRRs shows that reflectivity in the mixed phase region is up to 5.0–5.6 dB greater for CFs in polluted environments compared to CFs in pristine environments (holding thermodynamics fixed). This analysis favors a merged hypothesis for the simultaneous roles of thermodynamics and aerosols as they influence deep convective clouds in the Tropics.
63 citations
TL;DR: In this article, the authors used the GOES-R Advanced Baseline Imager (ABI) data, radar and lightning observations to analyze five convective storms, four of which were severe, to address uncertainties.
Abstract: The Geostationary Operational Environmental Satellite-14 (GOES-14) Imager operated in 1-min Super Rapid Scan Operations for GOES-R (SRSOR) mode during summer and fall of 2012 to emulate the high temporal resolution sampling of the GOES-R Advanced Baseline Imager (ABI). The current GOES operational scan interval is 15–30 min, which is too coarse to capture details important for severe convective storm forecasting including 1) when indicators of a severe storm such as rapid cloud-top cooling, overshooting tops, and above-anvil cirrus plumes first appear; 2) how satellite-observed cloud tops truly evolve over time; and 3) how satellite cloud-top observations compare with radar and lightning observations at high temporal resolution. In this paper, SRSOR data, radar, and lightning observations are used to analyze five convective storms, four of which were severe, to address these uncertainties. GOES cloud-top cooling, increased lightning flash rates, and peak precipitation echo tops often preceded seve...
TL;DR: In this article, the cloud-to-ground (CG) lightning climatology and its relationship to rainfall over central and eastern China is examined, using data from 32 million CG lightning flashes and Tropical Rainfall Measuring Mission measurements during a 6-yr period covering 2008-13.
Abstract: The cloud-to-ground (CG) lightning climatology and its relationship to rainfall over central and eastern China is examined, using data from 32 million CG lightning flashes and Tropical Rainfall Measuring Mission measurements during a 6-yr period covering 2008–13. Results show substantial spatial and temporal variations of flash density across China. Flash counts are the highest (lowest) in summer (winter) with the lowest (highest) proportion of positive flashes. CG lightning over northern China is more active only in summer, whereas in winter CG lightning is more active only in the Yangtze River basin. The highest CG lightning densities, exceeding 9 flashes per kilometer squared per year and more than 70 CG lightning days per year, are found in the northern Pearl River delta region, followed by the Sichuan basin, the Yangtze River delta, and the southeastern coast of China in that order. Lower-flash-density days occur over mountainous regions as a result of the development of short-lived afternoon...
TL;DR: In this article, the authors explored the climatologies of thunderstorm occurrence as seen by LIS and the conditional mean flash rates when thunderstorms do occur and found that the region where thunderstorms are seen most often by Lis extends slightly farther east in central Africa than the corresponding region with the highest total mean annual flash rates.
Abstract: The Lightning Imaging Sensor (LIS) on the Tropical Rainfall Measuring Mission (TRMM) satellite has previously been used to build climatologies of mean lightning flash rate across the global tropics and subtropics. This new work explores climatologies of thunderstorm occurrence as seen by LIS and the conditional mean flash rates when thunderstorms do occur. The region where thunderstorms are seen most often by LIS extends slightly farther east in central Africa than the corresponding region with the highest total mean annual flash rates. Presumably this reflects a difference between more frequent thunderstorm initiation in the east and upscale growth as storms move westward. There are some differences between locations with the greatest total lightning flash counts and those where thunderstorms occur most often. The greatest conditional mean flash rates—considering only those TRMM orbits that do have lightning in a given grid box—are found in subtropical regions. The highest values are in Argentina...
TL;DR: In this article, the authors used multiple dual-polarization Doppler radars across northern Alabama to quantify microphysical and kinematic properties and processes that often serve as precursors to lightning.
Abstract: The Deep Convective Clouds and Chemistry (DC3) experiment seeks to understand the kinematic and microphysical controls on the lightning behavior of deep moist convection. This study utilized multiple dual-polarization Doppler radars across northern Alabama to quantify microphysical and kinematic properties and processes that often serve as precursors to lightning, such as the graupel echo volume, graupel mass, and convective updraft volume. The focus here was on one multicellular complex that occurred on 21 May 2012 in northern Alabama during DC3. The graupel echo volume and the graupel mass in the charging region correlated well with the total lightning flash rate (FR), and even better than the updraft volumes and maximum updraft velocities. The flash length scales (LS) and flash areas were generally anticorrelated to the FR, while it was correlated to the nonprecipitation ice volume. More specifically, the presence of smaller flashes was associated with a stronger lower positive charge region ca...
TL;DR: In this paper, the authors examined changes in cloud-to-ground (CG) lightning characteristics over the decade 2003-12 using data from the National Lightning Detection Network (NLDN).
Abstract: Changes in lightning characteristics over the conterminous United States (CONUS) are examined to support the National Climate Assessment (NCA) program. Details of the variability of cloud-to-ground (CG) lightning characteristics over the decade 2003–12 are provided using data from the National Lightning Detection Network (NLDN). Changes in total (CG + cloud flash) lightning across part of the CONUS during the decade are provided using satellite Lightning Imaging Sensor (LIS) data. The variations in NLDN-derived CG lightning are compared with available statistics on lightning-caused impacts to various U.S. economic sectors. Overall, a downward trend in total CG lightning count is found for the decadal period; the 5-yr mean NLDN CG count decreased by 12.8% from 25 204 345.8 (2003–07) to 21 986 578.8 (2008–12). There is a slow upward trend in the fraction and number of positive-polarity CG lightning, however. Associated lightning-caused fatalities and injuries, and the number of lightning-caused wild...
TL;DR: In this paper, the onboard software configuration of the AGILE satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument.
Abstract: At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma-Ray Flashes (TGFs). The configuration change was highly successful resulting in an increase of one order of magnitude in TGF detection rate. As expected, the largest fraction of the new events has short duration (<100 μs), and part of them has simultaneous association with lightning sferics detected by the World Wide Lightning Location Network. The new configuration provides the largest TGF detection rate surface density (TGFs/km2/yr) to date, opening prospects for improved correlation studies with lightning and atmospheric parameters on short spatial and temporal scales along the equatorial region.
TL;DR: In this paper, the authors evaluated the performance of a recently developed cloud-scale lightning data assimilation technique implemented within the Weather Research and Forecasting Model running at convection-allowing scales (4-km grid spacing).
Abstract: This work evaluates the performance of a recently developed cloud-scale lightning data assimilation technique implemented within the Weather Research and Forecasting Model running at convection-allowing scales (4-km grid spacing). Data provided by the Earth Networks Total Lightning Network for the contiguous United States (CONUS) were assimilated in real time over 67 days spanning the 2013 warm season (May–July). The lightning data were assimilated during the first 2 h of simulations each day. Bias-corrected, neighborhood-based, equitable threat scores (BC-ETSs) were the chief metric used to quantify the skill of the forecasts utilizing this assimilation scheme. Owing to inferior observational data quality over mountainous terrain, this evaluation focused on the eastern two-thirds of the United States.During the first 3 h following the assimilation (i.e., 3-h forecasts), all the simulations suffered from a high wet bias in forecasted accumulated precipitation (APCP), particularly for the lightning...
TL;DR: A serendipitous recording of bidirectional lightning initiation in virgin air under the cloud base at ~11,000 images per second is reported, and the differences in characteristics of opposite polarity leader sections during the earliest stages of the discharge are reported.
Abstract: Lightning flashes are known to initiate in regions of strong electric fields inside thunderstorms, between layers of positively and negatively charged precipitation particles. For that reason, lightning inception is typically hidden from sight of camera systems used in research. Other technology such as lightning mapping systems based on radio waves can typically detect only some aspects of the lightning initiation process and subsequent development of positive and negative leaders. We report here a serendipitous recording of bidirectional lightning initiation in virgin air under the cloud base at ~11,000 images per second, and the differences in characteristics of opposite polarity leader sections during the earliest stages of the discharge. This case reveals natural lightning initiation, propagation and a return stroke as in negative cloud-to-ground flashes, upon connection to another lightning channel - without any masking by cloud.
TL;DR: In this article, the authors present a systematic analysis of the electromagnetic field inside a full-scale building associated with direct and nearby lightning strikes, taking into account the presence of reinforced concrete, to evaluate the effect of the structure of the reinforced concrete on the lightning electromagnetic fields.
Abstract: Lightning electromagnetic pulse (LEMP) is a severe threat to sensitive electronic devices installed in buildings. To protect these devices from LEMP effects, the evaluation of the electromagnetic fields inside of the building is required. Although numerous studies have been devoted to the analysis of these fields stemming from direct and indirect lightning strikes, no thorough study on the analysis of the electromagnetic environment inside a building with layered reinforcing bars has been presented in the past. In this paper, using the 3-D finite-difference time-domain method, we present a systematic analysis of the electromagnetic field inside a full-scale building associated with direct and nearby lightning strikes, taking into account the presence of reinforced concrete, to evaluate the effect of the structure of the reinforced concrete on the lightning electromagnetic fields.
TL;DR: In this article, the authors evaluated the Price and Rind lightning parameterization in the state-of-the-art Weather Research and Forecasting (WRF) model for the online simulation of lightning activity and found that the model-resolved variables related to the microphysics and thermodynamics are necessary for controlling the parameterization of lightning.
TL;DR: A fast-scanning phased array radar system installed in Osaka University has a temporal resolution of 10–30 s, which is much faster than the traditional weather radar and is ideal for observations of fast-evolving storm structures and the analysis of their relationship with lightning activities.
TL;DR: In this article, flash energy spectra were calculated from lightning mapping data collected during the 2009 Redoubt Volcano eruption and compared to the turbulence characteristics expected from each stage of plume development.
Abstract: The 2009 Redoubt Volcano eruption produced a series of explosive events, the largest of which produced episodes of volcanic lightning similar to thunderstorms. Flash energy spectra were calculated from lightning mapping data collected during the eruption. The spectra were compared to the turbulence characteristics expected from each stage of plume development. Small flash length scales present at early times were associated with the gas thrust and initial convective stages. Increases in flash length scales and flash energy as the explosive events progressed were associated with an increase in volume of the plume. Spectra with a large range in flash length scales (0.2–10 km) and a spectral peak at small flash length scales (< 1 km) were associated with a superposition of spectra from gas thrust, convective, and umbrella/ash cloud regions. An approximate 5/3 power law slope was observed on the order of 10 min after gas thrust forcing had ended and the transition to a drifting ash cloud was underway, which may reflect the dissipating state of the drifting ash cloud.
TL;DR: Transient luminous events include the upward electrical discharges from thunderstorms known as starters, jets, and gigantic jets as discussed by the authors, and electric discharges initiated in the lower ionosphere such as sprites, halos, and elves.
TL;DR: In this article, the authors investigated the shielding performance of different buildings in the presence of indirect lightning return strokes in the time domain by varying the channel geometrical characteristics and considering three different buildings.
Abstract: The shielding performance of different buildings in presence of indirect lightning return strokes are investigated directly in the time domain. To this end, a sensitivity analysis is conducted by varying the channel geometrical characteristics and considering three different buildings. The performance is evaluated by adopting the time-domain shielding parameters recently proposed, which appear to be suitable for shielding studies in presence of lightning electromagnetic pulses. The results confirm the usefulness of introducing different parameters to fully characterize the shielding behavior of buildings exposed to lightning electromagnetic fields.
TL;DR: In this article, a model capable of accounting for the local electric field increase in front of the lightning stepped leader up to magnitudes allowing front electrons to overcome the runaway energy threshold and thus to initiate relativistic runaway electron avalanches capable of generating X-ray and γ ray bursts observed in negative lightning leader.
Abstract: A model is proposed capable of accounting for the local electric field increase in front of the lightning stepped leader up to magnitudes allowing front electrons to overcome the runaway energy threshold and thus to initiate relativistic runaway electron avalanches capable of generating X-ray and γ ray bursts observed in negative lightning leader. The model is based on an idea that an ionization wave, propagating in a preionized channel, is being focused, such that its front remains narrow and the front electric field is being enhanced. It is proposed that when a space leader segment, formed ahead of a negative lightning leader, connects to the leader, the electric potential of the leader is transferred through the space leader in an ionizing wave that continues into the partly ionized channels of preexisting streamers of the space leader. It is shown with numerical simulations that the ionization channels of streamers limit the lateral expansion of the ionization wave, thereby enhancing the peak electric field to values allowing an acceleration of low-energy electrons into the runaway regime where electrons efficiently generate bremsstrahlung. The results suggest that the inhomogeneous ionization environment at the new leader tip amplifies the production rate of energetic electrons relative to a homogeneous environment considered in the past studies.
TL;DR: In this article, the authors used the World Wide Lightning Location Network along with tropical cyclone (TC) track and intensity data from the China Meteorological Administration to study lightning activity in TCs over the northwest Pacific from 2005 to 2009 and investigate the relationship between inner core lightning and TC intensity changes.
Abstract: Lightning data from the World Wide Lightning Location Network along with tropical cyclone (TC) track and intensity data from the China Meteorological Administration are used to study lightning activity in TCs over the northwest Pacific from 2005 to 2009 and to investigate the relationship between inner core lightning and TC intensity changes. Lightning in TCs over the northwest Pacific is more likely to occur in weak storms at tropical depression (10.8–17.1 m s−1) and tropical storm (17.2–24.4 m s−1) intensity levels, in agreement with past studies of Atlantic hurricanes. The greatest lightning density (LD) in the inner core appears in storms undergoing an intensity change of 15–25 m s−1 during the next 24 h. Lightning is observed in all storm intensity change categories: rapid intensification (RI), average intensity change (AIC), and rapid weakening (RW). The differences in LD between RI and RW are largest in the inner core, and the LD for RI cases is larger than for RW cases in the inner core (0–100 km). Lightning activity there, rather than in the outer rainbands, may be a better indicator for RI prediction in northwest Pacific storms. There was a marked increase in the lightning density of inner core during the RI stage for Super Typhoon Rammasun (2008). Satellite data for this storm show that the RI stage had the highest cloud top height and coldest cloud top temperatures, with all the minimum black body temperature values being below 200 K in the inner core.
TL;DR: In this paper, the authors proposed a new physical mechanism to explain the source of both IBPs and narrow bipolar events (NBEs) in lightning discharges, which is the electromagnetic transients associated with the sudden (i.e., stepwise) elongation of the initial negative leader extremity in the thunderstorm electric field.
Abstract: To date the true nature of initial breakdown pulses (IBPs) and narrow bipolar events (NBEs) in lightning discharges remains a mystery. Recent experimental evidence has correlated IBPs to the initial development of lightning leaders inside the thundercloud. NBE wideband waveforms resemble classic IBPs in both amplitude and duration. Most NBEs are quite peculiar in the sense that very frequently they occur in isolation from other lightning processes. The remaining fraction, 16% of positive polarity NBEs, according to Wu et al. (2014), happens as the first event in an otherwise regular intracloud lightning discharge. These authors point out that the initiator type of NBEs has no difference with other NBEs that did not start lightning, except for the fact that they occur deeper inside the thunderstorm (i.e., at lower altitudes). In this paper, we propose a new physical mechanism to explain the source of both IBPs and NBEs. We propose that IBPs and NBEs are the electromagnetic transients associated with the sudden (i.e., stepwise) elongation of the initial negative leader extremity in the thunderstorm electric field. To demonstrate our hypothesis a novel computational/numerical model of the bidirectional lightning leader tree is developed, consisting of a generalization of electrostatic and transmission line approximations found in the literature. Finally, we show how the IBP and NBE waveform characteristics directly reflect the properties of the bidirectional lightning leader (such as step length, for example) and amplitude of the thunderstorm electric field.
TL;DR: In this article, an electromagnetic model was used to simulate the response of tower-footing electrodes and overvoltages across insulators due to direct lightning strikes to the line, considering representative lightning current waveforms.
Abstract: This study assesses the lightning performance of 230- and 138-kV transmission lines under the assumptions of constant and frequency-dependent soil parameters. An electromagnetic model was used to simulate the response of tower-footing electrodes and overvoltages across insulators due to direct lightning strikes to the line, considering representative lightning current waveforms. Backflashover rates were determined using the Disruptive Effect Model. It was found that the decrease of soil resistivity and permittivity, resulting from the frequency-dependence effect, is responsible for significant decrease of the expected outage rate of the tested lines, in the range of 13–32% for usual distributions of soil resistivity along the lines.
TL;DR: In this paper, the authors focus on the climatology of cloud-to-ground (CG) lightning flashes based on PERUN lightning detection network data from 2002 to 2013 and analyze counts, density, polarity, peak current, and thunderstorm days.
Abstract: This research focuses on the climatology of cloud-to-ground (CG) lightning flashes based on PERUN lightning detection network data from 2002 to 2013. To present various CG lightning flash characteristics, 10 km × 10 km grid cells are used, while for estimating thunderstorm days, circles with radii of 17.5 km in the 1 km × 1 km grid cells are used. A total of 4 328 892 CG lightning flashes are used to analyze counts, density, polarity, peak current, and thunderstorm days. An average of 151 days with thunderstorm (appearing anywhere in Poland) occurs each year. The annual number of days with thunderstorms increases southeasterly from the coast of the Baltic Sea (15–20 days) to the Carpathian Mountains (30–35 days). The mean CG lightning flash density varies from 0.2 to 3.1 flashes km−2 yr−1 with the highest values in the southwest–northeast belt from Krakow-Czestochowa Upland to the Masurian Lake District. The maximum daily CG lightning flash density in this region amounted to 9.1 km−2 day−1 (3 July...
26 Oct 2015