Summer Lightning Research Articles

Upward Lightning at Wind Turbines: Risk Assessment From Larger-Scale Meteorology.

Upward lightning (UL) has become a major threat to the growing number of wind turbines producing renewable electricity. It can be much more destructive than downward lightning due to the large charge transfer involved in the discharge process. Ground-truth lightning current measurements indicate that less than 50% of UL could be detected by lightning location systems (LLS). UL is expected to be the dominant lightning type during the cold season. However, current standards for assessing the risk of lightning at wind turbines mainly consider summer lightning, which is derived from LLS. This study assesses the risk of LLS-detectable and LLS-undetectable UL at wind turbines using direct UL measurements at instrumented towers. These are linked to meteorological data using random forests. The meteorological drivers for the absence/occurrence of UL are found from these models. In a second step, the results of the tower-trained models are extended to a larger study area (central and northern Germany). The tower-trained models for LLS-detectable lightning are independently verified at wind turbine sites in this area and found to reliably diagnose this type of UL. Risk maps based on cold season case study events show that high probabilities in the study area coincide with actual UL flashes. This lends credibility to the application of the model to all UL types, increasing both risk and affected areas.

Melting and breaking characteristics of strands of high‐strength and high‐corrosion‐resistant OPGW due to DC arc discharge simulating high‐energy lightning strike

AbstractMetal strands of composite fiber‐optic ground wire (OPGW) are sometimes melted and broken by high‐energy lightning strikes. Direct current (DC) arc tests simulating the lightning strikes have thus been performed to obtain the melting and breaking characteristics of OPGW strands. J‐Power Transmission Network Co., Ltd. has developed high strength and high‐corrosion‐resistant OPGW for long‐span 500 kV overhead transmission lines crossing straits. This paper describes the melting and breaking characteristics of the OPGW strands due to DC arc discharge simulating high‐energy lightning strike. In this research, the tests were performed using two kinds of arc, one was the arc supposing summer lightning whose polarity was negative with a relatively short duration, and the other was the arc supposing winter lightning whose polarity was positive with a relatively long duration. Furthermore, the calculations regarding the melting and breaking of OPGW strands were carried out, and the calculation results showed a tendency similar to the test results.

Future increases in Arctic lightning and fire risk for permafrost carbon

Lightning is an indicator and a driver of climate change. Here, using satellite observations of lightning flash rate and ERA5 reanalysis, we find that the spatial pattern of summer lightning over northern circumpolar regions exhibits a strong positive relationship with the product of convective available potential energy (CAPE) and precipitation. Applying this relationship to Climate Model Intercomparison Project Phase 5 climate projections for a high-emissions scenario (RCP8.5) shows an increase in CAPE (86 ± 22%) and precipitation (17 ± 2%) in areas underlain by permafrost, causing summer lightning to increase by 112 ± 38% by the end of the century (2081–2100). Future flash rates at the northern treeline are comparable to current levels 480 km to the south in boreal forests. We hypothesize that lightning increases may induce a fire–vegetation feedback whereby more burning in Arctic tundra expedites the northward migration of boreal trees, with the potential to accelerate the positive feedback associated with permafrost soil carbon release. Changes in lightning activity are uncertain under climate change. The authors project that summer lightning in the Arctic is likely to more than double by the end of the century, with implications for lightning-strike tundra wildfires and associated carbon release from permafrost.

Change in the fire season pattern from bimodal to unimodal under climate change: The case of Daxing'anling in Northeast China

The length of the wildfire season has become longer in many regions around the world under climate change. This study investigated changes in fire season pattern (i.e., the number of separate periods of a year when wildfires are most likely to ignite, spread, and affect resources) and the contributions of climate change in Daxing'anling, Northeast China. An expanded fire dataset in both spatial and temporal converge from ground reporting was used. A comparison with satellite detected burned areas showed good agreement in spring, summer, and entire fire season. The results showed that the number of fires used to appear in a bimodal pattern with spring and fall peaks in the last century, but transitioned to a unimodal pattern peaked in summer in this century. This conversion was mainly resulted from a remarkable increase in summer lightning fires, which was in turned associated with warming in Daxing'anling. Another factor for the conversion was decreased spring nonlightning fire occurrence in the northwest subregion, where the conversion was the most significant. This decrease of fire was mainly associated with increased precipitation. The analysis of a compositional fire series, built as the log of the ratio of lightning to nonlightning fires, suggests that climate change was a major factor for the conversion of fire season pattern. The finding from this study indicates a need to adjust the fire prevention implementation timeline by including summer fires and to develop strategies to reduce the related risks to firefighter safety and forest ecosystem health in Daxing'anling.

Cloud-to-ground lightning flash density and the number of lightning flashes hitting wind turbines in Japan

The current status of the Japanese coastal region shows that winter lightning has seriously damaged wind turbines owing to its larger electrical charge than summer lightning. In Japan, 64% of serious wind turbine damage occurred in winter. Typically, lightning flash density is used to evaluate lightning risk in an area. Herein, we discuss the extent of lightning damage on wind turbines in Japan and cloud-to-ground (CG) lightning flash density based on the Japanese Lightning Detection Network, the largest lightning location system in Japan. Consequently, we found no correlation between the number of lightning flashes hitting wind turbines and summer lightning ground flash densities in the surrounding areas of a wind turbine. Approximately 95% of the lightning flashes that hit the turbine occurred in winter. The probabilities of lightning flashes hitting wind turbines were 0.12% in summer and 5.6% in winter. We developed a map showing the probability of lightning flashes hitting wind turbines in Japan. The probabilities obtained using this map were quite similar to the CG lightning flash density in winter. Therefore, we propose that lightning risk for wind turbines should not be evaluated based on the annual CG lightning flash density in Japan.

Three‐dimensional radio images of winter lightning in japan and characteristics of associated charge structure

We conducted lightning observational campaigns using a three‐dimensional (3D) lightning mapper called the Broadband Observation network for Lightning and Thunderstorms (BOLT) and C‐band radar to further understand the distinct characteristics of winter lightning in the coastal area of the Sea of Japan. We succeeded in locating 3D intracloud (IC) flashes, cloud‐to‐ground (CG) flashes, and upward lightning during winter. The basic characteristics of winter lightning, such as leader speeds and charge structure associated with an IC discharge, are similar to summer lightning. A noticeable difference between the winter lightning and the summer lightning is that the altitudes of the source locations associated with winter lightning are substantially lower than those associated with summer lightning. We performed a statistical comparison of winter and summer lightning. This comparison shows that the BOLT source altitude distributions during winter and summer peak at 2.1 and 7.5 km, respectively. Conversely, the distributions of the BOLT temperatures, which are the temperatures corresponding to the BOLT source altitudes, during both winter and summer show similar trends and have large values near −10 °C. These results indicate that a similar charge separation process, likely a noninductive charging mechanism, primarily contributes to thunderstorm electrification during both winter and summer. We show that the horizontal extent of the winter flashes is substantially larger than that of the summer flashes. This result implies that the charge regions in winter thunderstorms cover a wide area and, therefore, produce CG flashes with large charge transfers. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Influence of the Atmospheric Phenomena on the Tropospheric Delay of Satellite Navigation Signals

An error in calculating the tropospheric delay of satellite navigation signals is estimated for different atmospheric phenomena. As atmospheric phenomena, different precipitation types (hydrometeors) and electrical phenomena (thunderstorms and summer lightning) are considered. The tropospheric delay is calculated for the Saastamoinen and Hopfield models with the vertical profiles of the atmospheric meteorological parameters obtained by aerological sounding. The error of the given methods is determined by a comparison of the calculated and true values of the zenith tropospheric delays. The influence of the atmospheric phenomena on the error value is analyzed.

Spatio-temporal dimension of lightning flashes based on three-dimensional Lightning Mapping Array

3D mapping system like the LMA - Lightning Mapping Array - are a leap forward in lightning observation. LMA measurements has lead to an improvement on the analysis of the fine structure of lightning, allowing to characterize the duration and maximum extension of the cloud fraction of a lightning flash. During several years of operation, the first LMA deployed in Europe has been providing a large amount of data which now allows a statistical approach to compute the full duration and horizontal extension of the in-cloud phase of a lightning flash. The “Ebro Lightning Mapping Array” (ELMA) is used in the present study. Summer and winter lighting were analyzed for seasonal periods (Dec–Feb and Jun–Aug). A simple method based on an ellipse fitting technique (EFT) has been used to characterize the spatio-temporal dimensions from a set of about 29,000 lightning flashes including both summer and winter events. Results show an average lightning flash duration of 440ms (450ms in winter) and a horizontal maximum length of 15.0km (18.4km in winter). The uncertainties for summer lightning lengths were about ± 1.2km and ± 0.7km for the mean and median values respectively. In case of winter lightning, the level of uncertainty reaches up to 1km and 0.7km of mean and median value. The results of the successful correlation of CG discharges with the EFT method, represent 6.9% and 35.5% of the total LMA flashes detected in summer and winter respectively. Additionally, the median value of lightning lengths calculated through this correlative method was approximately 17km for both seasons. On the other hand, the highest median ratios of lightning length to CG discharges in both summer and winter were reported for positive CG discharges.

Electrostatic model to understand the influence of salt deposit in gfrp material during lightning discharges

A methodical experimentation and mathematical modeling is carried out to study the influence of salt deposit on wind turbine blade material (Glass Fiber Reinforced Plastics/GFRP) during lightning discharges. Electrical discharge measurements combined with optical emission spectroscopy technique and electrostatics is utilized to understand the dynamics of surface discharge and the level of damage on GFRP material. COMSOL simulation studies shows that the electric field intensity on the surface of the polluted GFRP gets enhanced when compared to that of virgin GFRP, irrespective of the applied voltage profile and polarity. Flashover voltage, discharge current and optical emission spectroscopy measurements indicates that the deterioration of GFRP material is severe when there is an adhesion of salt deposit. It is also observed that the damage induced on GFRP material is severe for winter lightning (switching impulse voltage of 250/2500 μs) compared to that of summer lightning (lightning impulse voltage of 1.2/50 μs) due to a longer front and tail period of the pulse.

An Environment and Ionosphere to Examining Optical and Radio of Lightning-Related Wonders

The observing as well as sounding of lightning releases and their related phenomea (mesospheric optical outflows and so on.) has been performed by radio and optical estimations. We focus on the winter lightning in the Hokuriku region (Japan Sea side) of Japan, since it is critical to explore whether lighting releases in the Hokuriku territory (entire spatial scale is generally little in correlation with the traditional summer lightning in the US) could trigger the mesospheric optical emanations. The optical perception of those mesospheric emanations and the comparing radio sounding by ELF and VHF radio waves of their parent lightning, have been accounted for. The watching frameworks are initially exhibited, and our most recent observational certainties on the mesospheric outflows in the Hokuriku territory, their parent lightning and some PC recreations on the sprite start, are introduced.

Seasonal, Monthly, and Weekly Distributions of NLDN and GLD360 Cloud-to-Ground Lightning

Abstract Annual maps of cloud-to-ground lightning flash density have been produced since the deployment of the National Lightning Detection Network (NLDN). However, a comprehensive national summary of seasonal, monthly, and weekly lightning across the contiguous United States has not been developed. Cloud-to-ground lightning is not uniformly distributed in time, space, or frequency. Knowledge of these variations is useful for understanding meteorological processes responsible for lightning occurrence, planning outdoor events, anticipating impacts of lightning on power reliability, and relating to severe weather. To address this gap in documentation of lightning occurrence, the variability on seasonal, monthly, and weekly scales is first addressed with NLDN flash data from 2005 to 2014 for the 48 states and adjacent regions. Flash density and the percentage of each season’s portion of the annual total are compiled. In spring, thunderstorms occur most often over southeastern states. Lightning spreads north and west until by June, most areas have lightning. New England, the northern Rockies, most of Canada, and the Florida Peninsula have a small percentage of lightning outside of summer. Arizona and portions of adjacent states have the highest incidence in July and August. Flash densities reduce in September in most regions. This seasonal, monthly, and weekly overview complements a recent study of diurnal variations of flashes to document when and where lightning occurs over the United States. NLDN seasonal maps indicate a summer lightning dominance in the northern and western United States that extends into Canada using data compiled from GLD360 network observations. GLD360 also extends NLDN seasonal maps and percentages into Mexico, the Caribbean, and offshore regions.

Summer lightning: a guide to the Second Battle of Manassas

Summer lightning: a guide to the Second Battle of Manassas

The structure of X‐ray emissions from triggered lightning leaders measured by a pinhole‐type X‐ray camera

We investigate the structure of X‐ray emissions from downward triggered lightning leaders using a pinhole‐type X‐ray camera (XCAM) located at the International Center for Lightning Research and Testing. This study builds on the work of Dwyer et al. (2011), which reported results from XCAM data from the 2010 summer lightning season. Additional details regarding the 2010 data are reported here. During the 2011 summer lightning season, the XCAM recorded 12 out of 17 leaders, 5 of which show downward leader propagation. Of those five leaders, one dart‐stepped leader and two chaotic dart leaders are the focus of this paper. These three leaders displayed unique X‐ray emission patterns: a chaotic dart leader displayed a diffuse structure (i.e., a wide lateral “spraying” distribution of X‐rays), and a dart‐stepped leader and a chaotic dart leader exhibited compact emission (i.e., a narrow lateral distribution of strong X‐ray emission). These two distinct X‐ray emission patterns (compact and diffuse) illustrate the variability of lightning leaders. Using Monte Carlo simulations, we show that the diffuse X‐ray source must originate from a diffuse source of energetic electrons or possibly emission from several sources. The compact X‐ray sources originate from compact electron sources, and the X‐ray source region radius and electric charge contained within the X‐ray source region were between 2 and 3 m and on the order of 10–4 C, respectively. For the leaders under investigation, the X‐ray source region average currents were determined to be on the order of 102 A.

Measurement of Energy Absorption Capability of Distribution Surge Arresters by Natural Winter Lightning Current

Surge arresters and distribution equipments with zinc-oxide (ZnO) elements are used for lightning protection of overhead power distribution lines in Japan. The increase of surge arresters including distribution equipments with ZnO elements has resulted in a remarkable decrease of lightning outages of distribution lines due to sparkover. On the other hand, these surge arresters are sometimes damaged by direct lightning strokes, especially in winter. Winter lightning strokes have very large electric charge as compared with summer lightning strokes. For improvement of surge arresters, we have measured the energy absorption capability of surge arresters using natural winter lighting strokes to a test tower. The energy absorption capability of an insulator with built-in ZnO elements is about 1.4 times larger than that of a surge arrester with the same ZnO elements. The ZnO elements of the insulator are wrapped in an insulation sheet in order to fix ZnO elements in the center of the porcelain housing because the insulators are installed horizontally. The insulation sheet strengthens insulation of the side of ZnO elements, and the energy absorption capability of the insulator improves. The result indicates that wrapping ZnO elements in the insulation sheet is one of effective countermeasures against surge arrester failures.

The Slow-Varying Electric Field of Negative Upward Lightning Initiated by the Peissenberg Tower, Germany

This paper analyzes the slow-varying electric fields and the associated currents of a total of 35 negative upward lightning initiated by the Peissenberg tower, Germany. Thirty-four of which were from winter upward lightning and only one from summer upward lightning. It appears that all of the winter upward lightning were initiated without nearby preceding lightning activity (called “self-initiated” lightning) and only the summer lightning was triggered by nearby lightning activity (called “other-triggered” lightning). The slow-varying electric fields of the winter upward lightning showed a fast rise characterized by the 10-90% risetime, with an arithmetic mean of 13.8 ms. After attaining the maximum, the electric field turned into a slow decay being characterized by the time on half value which was evaluated to having the arithmetic mean of 441 ms. Transported charges to ground were on average 44.8 C and on maximum 165 C. The maximum value of the electric field was 39.9 kV/m on average, with the highest value being 64.5 kV/m. For the electric fields, higher values were prevented by recovery effects such as the corona from objects at ground and the redistribution of the charge in the thundercloud. Due to these effects, no or only weak correlations were found between the 10-90% risetime, the time on half value, the charge, and the maximum of the electric field. From additional measurements with a field mill, it was found that the electric field recovers to the starting level within some seconds.

Seasonal variations in the lightning diurnal cycle and implications for the global electric circuit

Data obtained from the Optical Transient Detector and the Lightning Imaging Sensor satellites (70° and 35° inclination low earth orbits, respectively) are used to statistically determine the number of flashes in the seasonal diurnal cycle as a function of local and universal time. These data include corrections for detection efficiency and instrument view time. They are further subdivided by season, land versus ocean, and other spatial (e.g., continents) and temporal (e.g., time of peak diurnal amplitude) categories. These statistics are then combined with analyses of high altitude aircraft observations of electrified clouds to produce the seasonal diurnal variation in the global electric circuit. Continental results display strong diurnal variation, with a lightning peak in the late afternoon and a minimum in late morning. In geographical regions dominated by large mesoscale convective systems, the peak in the diurnal curve shifts toward late evening or early morning hours. The maximum seasonal diurnal flash rate occurs in June–August, corresponding to the Northern Hemisphere summer, while the minimum occurs in December–February. Summer lightning dominates over winter activity and springtime lightning dominates over fall activity at most continental locations. Oceanic lightning exhibits minimal diurnal variation, but morning hours are slightly enhanced over afternoon. As was found earlier, for the annual diurnal variation, using basic assumptions about the mean storm currents as a function of flash rate and location (i.e., land/ocean), our seasonal estimates of the current in the global electric circuit provide an excellent match with independent measurements of the seasonal Carnegie curve diurnal variations. The maximum (minimum) total mean current of 2.4kA (1.7kA) is found during Northern Hemisphere summer (winter). Land thunderstorms supply about one half (52%) of the total global current. Ocean thunderstorms contribute about one third (31%) and the non-lightning producing ocean electrified shower clouds (ESCs) supply one sixth (15%) of the total global current. Land ESCs make only a small contribution (2%).

Development of Lightning-Resistant Overhead Ground Wire for Large-size Transmission Lines

The overhead ground wire of AC 150mm2 is applied for the large-size transmission lines. According to inspections of transmission lines, melted component wires of AC 150mm2 have been found in some parts of 500kV transmission lines and it is obvious that the damages have been caused by lightning. Hence, the authors have developed lightning-resistant overhead ground wires as well as being evaluated lightning-resistant performance of the conventional AC 150mm2. In the paper, firstly, it is reported on the lightning performance of the conventional AC 150mm2 resulting from a DC arc test which is considered the polarity of currents and injected current waveforms for summer and winter lightning. As a result, the least amount of electric charges which can melt the components of the conventional wire was 180C. Then, the paper outlines the improvement of lightning performance of the overhead ground wire. Some kinds of developed ground wires as a trial piece have been proposed and tested, and here presented the characteristics of two typical developed wires among them. One is coated with conductive ceramic on the outer components and the another is enlarged a diameter of outer components. Both types of the wires show the excellent lightning performance from the DC arc test, comparing with the conventional ground wire of AC 150mm2.

2006-2007년 여름 사례로 본 구름-지면 낙뢰와 강우의 관계

본 연구에서는 2006-2007년 여름(6-8월)동안의 기상청 낙뢰 관측자료와 자동관측소 강우량 자료를 사용하여 여름철 낙뢰와 강우의 관계에 대해 분석하였다. 대부분의 부극성 낙뢰는 대류가 활발한 중심에 집중되어 발생하고 낙뢰빈도가 높고 강한 강우를 동반하였다. 반면 대부분의 정극성 낙뢰는 구름의 가장자리 또는 모루운에서 발생하고 낙뢰빈도는 낮으며, 약한 강우를 동반하였다. 일반적으로 강우강도는 부극성과 정극성이 함께 발생했을 경우 가장 강하고 부극성 낙뢰, 정극성 낙뢰, 그리고 낙뢰가 발생하지 않은 순으로 나타나고 있다. 여름철 전체 낙뢰 중 정극성 낙뢰의 비율은 평균 10% 이하이며 강우를 유발하지 않는 낙뢰의 비율은 평균 34%이다. 강우강도는 특히 부극성 낙뢰빈도와 높은양의 상관을 보였고, 낙뢰는 강우와 동시에 발생하거나 약 10분정도 선행하는 경향을 보였다. 낙뢰를 동반한 강우를 대류성 강우로 정의하여 분석한 결과 우리나라 여름철 강우 중 적어도 20% 이상은 대류성 강우이며 6, 7월보다는 8월에 대류성 강우가 많이 발생하고 있다. 또한 강우 및 낙뢰와 같이 대류성 강우의 비율도 오후에 최대치를 보이는 일변동을 보인다. A relationship between cloud-to-ground lightning and rainfall was investigated by using the two-years (2006-2007) summer lightning data and the automatic weather stations (AWSs) data of the Korea Meteorological Administration. The negative lightning occurred at the core of highly concentrated convection, which is often accompanied with heavy rains. Whereas most positive lightning occurred at the anvil cloud with low density and light rains. The rainfall intensity is strongest when the negative and positive lightning occurred concurrently, and one with lightning is much stronger than that without lightning. A portion of the positive lightning of the total lightning was less than 10% during summer seasons, and the lightning without rains was about 34%. The rain rate was strongly correlated with the negative flash rate, and the correlation coefficients varied between 0.87 and 0.94 according to the co-location radius (5-15 km) of AWSs. Most of the lightning occurred 10 minutes before and/or concurrently occurred with rains. A portion of the convective rainfalls of the total rainfalls was at least 20% when we define the rainfalls with lightning as convective. The convective rainfall was greater during August than in June and July. In general, the portion of convective rainfalls showed a maximum diurnal variation during late afternoon as in the rains and lightning.

Outage Rates of Power Distribution Lines due to Summer and Winter Lightning in Chugoku Region

Taking the densities of lightning strokes and electric poles into account, we calculated outage rates of each equipment on a 6.6kV distribution line due to summer (Mar.-Oct.) and winter (Nov.-Feb.) lightning for 6 years in the Chugoku region located in the western part of Japan. Furthermore, using these results, we proposed some application maps for the lightning risk assessment of power distribution lines in this region considering the effect of seasonal lightning hazard.

Analyses of summer lightning activity and precipitation in the Central and Eastern Mediterranean

The lightning activity and precipitation in two 3-hour time intervals in the grid boxes of 0.25 × 0.25° over East and Central Mediterranean during the summer of 2005 and 2006 are analysed. The results show that the frequency distribution of the precipitation amount is shifted towards larger values for the cases with lightning as compared with the cases without lightning. It was found that the number of cases with 3-hour accumulated rainfall greater than 10 mm was bigger when lightning occurred (65%) than when it was absent (35%). Investigation of diurnal and spatial distributions of lightning shows that the afternoon flash density peak is associated mainly with lightning over the land, which is in accordance with the results of earlier works. The early morning flash density peak is associated mainly with flashes over the sea. High correlation coefficients (0.89 during the morning hours and 0.98 during afternoon) were found between rain rate (mm/h) and average flash density (fl/km 2) when flash density is averaged in logarithmic intervals of rain rate.