The US National Lightning Detection Network/sup TM/ and applications of cloud-to-ground lightning data by electric power utilities
TL;DR: The US National Lightning Detection Network/sup TM/ (NLDN) as mentioned in this paper is a system that senses the electromagnetic fields that are radiated by individual return strokes in cloud-to-ground (CG) flashes.
Abstract: Lightning is a significant cause of interruptions or damage in almost every electrical or electronic system that is exposed to thunderstorms. The problem is particularly severe for electric power utilities that have exposed assets covering large areas. We summarize the basic properties of cloud-to-ground (CG) lightning, the primary hazard to structures on the ground, and then we discuss methods of detecting and locating such discharges. We describe the US National Lightning Detection Network/sup TM/ (NLDN), a system that senses the electromagnetic fields that are radiated by individual return strokes in CG flashes. This network provides data on the time of such strokes, their location and polarity and an estimate of the peak current. We discuss the network detection efficiency and location accuracy and some of the limitations that are inherent in any detection system that operates with a finite number of sensors with fixed trigger thresholds. We also discuss how NLDN data have benefited utilities by providing lightning warnings in real time and information on whether CG strokes are the cause of faults, documenting the response of fixed assets that are exposed to lightning, and quantifying the effectiveness of lightning protection systems. We conclude with some general observations on the use of lightning data by power utilities and we provide some guidelines on the uncertainties in lightning parameters that are acceptable in the industry.
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TL;DR: The history leading to modern LLSs that sense lightning radiation fields at multiple remote sensors, focusing on the interactions between enabling technology, scientific discovery, technical development, and uses of the data are described.
Abstract: Lightning in all corners of the world is monitored by one or more land- or space-based lightning locating systems (LLSs). The applications that have driven these developments are numerous and varied. This paper describes the history leading to modern LLSs that sense lightning radiation fields at multiple remote sensors, focusing on the interactions between enabling technology, scientific discovery, technical development, and uses of the data. An overview of all widely used detection and location methods is provided, including a general discussion of their relative strengths and weaknesses for various applications. The U.S. National Lightning Detection Network (NLDN) is presented as a case study, since this LLS has been providing real-time lightning information since the early 1980s, and has provided continental-scale (U.S.) information to research and operational users since 1989. This network has also undergone a series of improvements during its >20-year life in response to evolving detection technologies and expanding requirements for applications. Recent analyses of modeled and actual performance of the current NLDN are also summarized. The paper concludes with a view of the short- and long-term requirements for improved lightning measurements that are needed to address some open scientific questions and fill the needs of emerging applications.
586 citations
TL;DR: In this article, a review and comparison of alternative data sources and approaches for mapping fire regimes at national, regional, and local spatial scales is presented, which is useful for strategically planning fire and natural resource management, assessing risk and ecological conditions, illustrating change in disturbance regimes through time, identifying knowledge gaps, and learning how climate, topography, vegetation and land use influence fire regimes.
Abstract: This paper was presented at the conference ‘Integrating spatial technologies and ecological principles for a new age in fire management’, Boise, Idaho, USA, June 1999 Maps of fire frequency, severity, size, and pattern are useful for strategically planning fire and natural resource management, assessing risk and ecological conditions, illustrating change in disturbance regimes through time, identifying knowledge gaps, and learning how climate, topography, vegetation, and land use influence fire regimes. We review and compare alternative data sources and approaches for mapping fire regimes at national, regional, and local spatial scales. Fire regimes, defined here as the nature of fires occurring over an extended period of time, are closely related to local site productivity and topography, but climate variability entrains fire regimes at regional to national scales. In response to fire exclusion policies, land use, and invasion of exotic plants over the last century, fire regimes have changed greatly, especially in dry forests, woodlands, and grasslands. Comparing among and within geographic regions, and across time, is a powerful way to understand the factors determining and constraining fire patterns. Assembling spatial databases of fire information using consistent protocols and standards will aid comparison between studies, and speed and strengthen analyses. Combining multiple types of data will increase the power and reliability of interpretations. Testing hypotheses about relationships between fire, climate, vegetation, land use, and topography will help to identify what determines fire regimes at multiple scales.
375 citations
TL;DR: In this paper, the authors used the time of group arrival (TOGA) of the VLF (3-30 kHz ) radiation from a lightning stroke to locate lightning.
315 citations
TL;DR: In this article, an analysis of electric and magnetic fields radiated by lightning first and subsequent return strokes to tall towers is presented, and the results have important implications in electromagnetic compatibility.
Abstract: An analysis of electric and magnetic fields radiated by lightning first and subsequent return strokes to tall towers is presented. The contributions of the various components of the fields, namely, static, induction, and radiation for the electric field, and induction and radiation for the magnetic field are illustrated and discussed. It is shown in particular that the presence of a tower tends, in general, to increase substantially the electric and magnetic field peaks and their derivatives. This increase is mainly caused by the presence of two oppositely propagating current wavefronts originating from the tower top and by the very high propagation velocity of current pulses within the tower, and depends essentially on the wavefront steepness of the channel-base current. Because of the last factor, the increase of the field magnitudes is found to be significantly higher for subsequent return strokes, which are characterized by much faster risetimes compared to first return strokes. The presented results are consistent with experimental observations of current in lightning strokes to the Toronto CN Tower and of the associated electric and magnetic fields measured 2 km away. These findings partially explain the fact that subsequent return strokes characterized by lower current peaks but higher front steepnesses and return stroke speeds may result in higher field peaks. The results obtained have important implications in electromagnetic (EM) compatibility. It is found that lightning strokes to tall metallic objects lead to increased EM field disturbances. Also, subsequent return strokes are to be considered an even more important source of EM interference than first return strokes. Indeed, EM fields from subsequent strokes are characterized by faster fronts and additionally, they may reach greater peaks than first strokes. Lastly, findings of this study emphasize the difficulty of extracting reliable lightning return stroke current information from remote EM field measurements using oversimplified formulae.
307 citations
TL;DR: In this paper, the statistical data of the significant parameters of lightning flash, collected by many researchers over many years around the world, are presented, including peak current, waveshape and velocity of the return stroke, the total flash charge and /spl int/I/sup 2/dt.
Abstract: The paper presents the statistical data of the significant parameters of lightning flash, collected by many researchers over many years around the world. The significant parameters of a lightning flash are: peak current, waveshape and velocity of the return stroke, the total flash charge and /spl int/I/sup 2/dt. Negative first strokes have traditionally been considered to produce the worst stress on the system insulation. The subsequent negative strokes have significantly lower peak current but shorter wavefronts. This may stress the system insulation more. The positive strokes have about the same median current value as the negative first strokes and longer fronts, thus producing less stress. However, their duration is longer than that of the negative strokes. Therefore, the system insulation may be damaged because of the lower volt-time characteristic for long-duration waves. The positive strokes may also cause more thermal damage because of their significantly higher charge and /spl int/I/sup 2/dt. The relationship between the return-stroke velocity and the current peak is a significant parameter in estimating lightning-induced voltages and also in estimating the peak current from the radiated electromagnetic fields of the lightning channel. For better accuracy, the current and the velocity should be measured simultaneously. Better methods to measure the stroke current need to be developed. Correlation coefficient between various lightning parameters is another important parameter which will affect the analysis significantly. Lightning characteristics should be classified according to geographical regions and seasons instead of assuming these characteristics to be globally uniform.
272 citations
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TL;DR: The U.S. National Lightning Detection Network (NLDN) has provided real-time and historical lightning data to the electric utility industry, the National Weather Service, and other government and commercial users.
Abstract: The U.S. National Lightning Detection Network TM (NLDN) has provided lightning data covering the continental United States since 1989. Using information gathered from more than 100 sensors, the NLDN provides both real-time and historical lightning data to the electric utility industry, the National Weather Service, and other government and commercial users. It is also the primary source of lightning data for use in research and climatological studies in the United States. In this paper we discuss the design, implementation, and data from the time-of-arrival/magnetic direction finder (TOA/MDF) network following a recent system-wide upgrade. The location accuracy (the maximum dimension of a confidence region around the stroke location) has been improved by a factor of 4 to 8 since 1991, resulting in a median accuracy of 500 m. The expected flash detection efficiency ranges from 80% to 90% for those events with peak currents above 5 kA, varying slightly by region. Subsequent strokes and strokes with peak currents less than 5 kA can now be detected and located; however, the detection efficiency for these events is not quantified in this study because their peak current distribution is not well known.
1,010 citations
TL;DR: Several aspects of the calculation of lightning electric and magnetic fields in which return stroke models are used to specify the source are considered, including equations for fields and channel-base current, as well as a discussion of channel tortuosity and branches.
Abstract: Four classes of models of the lightning return stroke are reviewed. These four classes are: (1) the gas dynamic models; (2) the electromagnetic models; (3) the distributed-circuit models; and (4) the "engineering" models. Validation of the reviewed models is discussed. For the gas dynamic models, validation is based on observations of the optical power and spectral output from natural lightning. The electromagnetic, distributed-circuit, and "engineering" models are most conveniently validated using measured electric and magnetic fields from natural and triggered lightning. Based on the entirety of the validation results and on mathematical simplicity, we rank the "engineering" models in the following descending order: MTLL, DU, MTLE, BG, and TL. When only the initial peak values of the channel-base current and remote electric or magnetic field are concerned, the TL model is preferred. Additionally discussed are several issues in lightning return-stroke modeling that either have been ignored to keep the modeling straightforward or have not been recognized, such as the treatment of the upper, in-cloud portion of the lightning channel, the boundary conditions at the ground, including the presence of a vertically extended strike object, the return-stroke speed at early times, the initial bi-directional extension of the return stroke channel, and the relation between leader and return stroke models. Various aspects of the calculation of lightning electric and magnetic fields in which return stroke models are used to specify the source are considered, including equations for fields and channel-base current, as well as a discussion of channel tortuosity and branches.
529 citations
TL;DR: For the case of a finite linear antenna along which a fixed current waveform propagates, the authors presented analytical time−domain solutions for the electric and magnetic radiation (far) fields.
Abstract: Textbooks rarely give time−domain solutions to antenna problems. For the case of a finite linear antenna along which a fixed current waveform propagates, we present analytical time−domain solutions for the electric and magnetic radiation (far) fields. We also give computer solutions for the total (near and far) fields. The current waveform used as an example in the computer calculations approximates that of a lightning return−stroke, a common geophysical example of the type of radiation source under consideration.
486 citations