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.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD00153

A Combined TOA/MDF Technology Upgrade of the U.S. National Lightning Detection Network

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.

/pdf/review-and-evaluation-of-lightning-return-stroke-models-198e2ag3lz.pdf

Review and evaluation of lightning return stroke models including some aspects of their application

Evidence for the tripole structure of electrified clouds is summarized. The observed structure is quantitatively consistent with the results of laboratory simulations and suggests that collision between ice crystals and rimed graupel particles is the dominant mechanism for charge separation in thunderstorms. The physical basis for this mechanism is poorly understood.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/JD094iD11p13151%4010.1002/%28ISSN%292169-8996.ELECCONF2

The tripole structure of thunderstorms

Compares five lightning return stroke current models that exhibit a simple relationship between the current at the return stroke channel-base and the current along the return stroke channel, namely the Bruce-Golde (BG) model, the transmission line (TL) model, the Master, Uman, Lin, and Standler (MULS) model, the Traveling Current Source (TCS) model, and the Modified Transmission Line (MTL) model, by assuming a common current wave shape at the channel base and then calculating the channel currents and charges and the resultant electric and magnetic fields. Two characteristics distinguish the models: the treatment of the return stroke wave front, and the spatial and temporal distribution of charge removed from the leader channel. The TL model is unrealistic for long-time field calculations owing to the fact that no net charge is removed from the channel. The other four models produce overall fields which are reasonable approximations to measured fields from natural lightning

Lightning return stroke current models with specified channel‐base current: A review and comparison

The new expression of the lightning current at the striking point is analyzed. The basic four channel-base lightning current quantities are assumed to be known: current peak value, current rise-time, maximum of the current steepness and the charge transfer at the striking point. The algorithm for a fast calculation of the channel-base current parameters is proposed. The numerical example of the current parameters determination is given. The proposed algorithm can be successfully used for the lightning current modelling in power engineering as well as in the research of the radiated lightning electromagnetic pulse and its coupling with the overhead lines and other metallic structures.

Calculation of lightning current parameters

The “transmission-line model” of return-stroke radiation, proposed by Uman and McLain (1970), has been tested on rocket-triggered lightning Simultaneous measurements are reported of electric radiation field, current at the channel base, and stroke-propagation velocity Agreement between model and measurements is generally good during the first few microseconds, although several anomalies are pointed out Truncation of the sharp initial peak in many of the field waveforms, motivated by the hypothesis that the return stroke begins a short distance above the ground, leads to an average apparent velocity (derived from the ratio of peak field to peak current) of (151±017) × 108 m/s for 28 strokes, in excellent agreement with the average, photographically measured two-dimensional velocity of (152±017) × 108 m/s for 18 of these same strokes Although the correlation between apparent and photographic velocities for these 18 strokes is poor, the uncertainty in the photographic velocity determinations could explain most of the scatter The best formula for estimating peak currents (ip) in subsequent return strokes from remotely measured, truncated peak electric fields (E′p) at range D appears to be ip = −39 × 10−2 DE′p − 27 × 103, where all variables are in MKS units and the electric field polarity of return strokes lowering negative charge is considered negative

Submicrosecond intercomparison of radiation fields and currents in triggered lightning return strokes based on the transmission-line model

Peak currents, two-dimensional average propagation speeds, and electric field waveforms for a number of subsequent return strikes in rocket-triggered lightning flashes were measured in order to test the 'transmission-line model' of return-stroke radiation of Uman and McLain (1970). Reasonable agreement is found between the propagation speeds measured with the streak camera and those deduced from the transmission-line model. A modification of the model is proposed in which two wave fronts travel upward and downward away from a junction point a short distance above the ground.

An experimental test of the 'transmission-line model' of electromagnetic radiation from triggered lightning return strokes

Triggered lightning experiments with rockets pulling a grounded wire were performed at Langmuir Laboratory in 1981. Out of 56 firings, 35 events were triggered among which 29 had a peak current intensity above 2 kA and 27 were hybrid flashes. The highest current peak is 40 kA±10%. The median value of the transported charge is 35 C, including a contribution of 28 C from the continuous component. The largest charge is in a flash carrying a mixture of +235 and −240 C±10%. The median number of pulses is 15 above 2 kA, 10 above 3 kA, and 2 above 10 kA. Comparison with natural lightning reveals a large excess of small current pulses in the triggered case, but there is a great similarity in shape, size, and number between the subsequent strokes of natural flashes and the largest among the pulses in the triggered events.

Triggered lightning in New Mexico

Three triggered lightning flashes, initiated during the Thunderstorm Research International Program (1981) at Langmuir Laboratory, New Mexico, are examined on the basis of three-dimensional return stroke propagation speeds and peak currents. Nonlinear relationships result between return stroke propagation speed and stroke peak current for 56 strokes, and between return stroke propagation speed and dart leader propagation speed for 32 strokes. Calculated linear correlation coefficients include dart leader propagation speed and ensuing return stroke peak current (32 strokes; r = 0.84); and stroke peak current and interstroke interval (69 strokes; r = 0.57). Earlier natural lightning data do not concur with the weak positive correlation between dart leader propagation speed and interstroke interval. Therefore, application of triggered lightning results to natural lightning phenomena must be made with certain caveats. Mean values are included for the three-dimensional return stroke propagation speed and for the three-dimensional dart leader propagation speed.

Correlated observations of three triggered lightning flashes

The invention concerns an improvement to devices for the firing of blasting charges in order to trigger deliberate avalanches. It consists in transmitting on the electrical transmission line which is constituted by the metal carrying cable 1, a selection of one out of several possible encoded signals. Each blasting charge 15 is capable of receiving only one of these signals. It is thus possible to control selectively one or more of these charges.

L. Barret

Papers

Submicrosecond intercomparison of radiation fields and currents in triggered lightning return strokes based on the transmission-line model

An experimental test of the 'transmission-line model' of electromagnetic radiation from triggered lightning return strokes

Triggered lightning in New Mexico

Correlated observations of three triggered lightning flashes

Installation for the transport and selective remote firing of several blasting charges carried by a carrying cable.