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.

An Overview of Lightning Locating Systems: History, Techniques, and Data Uses, With an In-Depth Look at the U.S. NLDN

Quasi-electrostatic (QE) fields that temporarily exist at high altitudes following the sudden removal (e.g., by a lightning discharge) of thundercloud charge at low altitudes lead to ambient electron heating (up to ∼5 eV average energy), ionization of neutrals, and excitation of optical emissions in the mesosphere/lower ionosphere. Model calculations predict the possibility of significant (several orders of magnitude) modification of the lower ionospheric conductivity in the form of depletions of electron density due to dissociative attachment to O2 molecules and/or in the form of enhancements of electron density due to breakdown ionization. Results indicate that the optical emission intensities of the 1st positive band of N2 corresponding to fast (∼ 1 ms) removal of 100–300 C of thundercloud charge from 10 km altitude are in good agreement with observations of the upper part (“head” and “hair” [Sentman et al., 1995]) of the sprites. The typical region of brightest optical emission has horizontal and vertical dimensions ∼10 km, centered at altitudes 70 km and is interpreted as the head of the sprite. The model also shows the formation of low intensity glow (“hair”) above this region due to the excitation of optical emissions at altitudes ∼ 85 km during ∼ 500 μs at the initial stage of the lightning discharge. Comparison of the optical emission intensities of the 1st and 2nd positive bands of N2, Meinel and 1st negative bands of , and 1st negative band of demonstrates that the 1st positive band of N2 is the dominating optical emission in the altitude range around ∼70 km, which accounts for the observed red color of sprites, in excellent agreement with recent spectroscopic observations of sprites. Results indicate that the optical emission levels are predominantly defined by the lightning discharge duration and the conductivity properties of the atmosphere/lower ionosphere (i.e., relaxation time of electric field in the conducting medium). The model demonstrates that for low ambient conductivities the lightning discharge duration can be significantly extended with no loss in production of optical emissions. The peak intensity of optical emissions is determined primarily by the value of the removed thundercloud charge and its altitude. The preexisting inhomogeneities in the mesospheric conductivity and the neutral density may contribute to the formation of a vertically striated fine structure of sprites and explain why sprites often repeatedly occur in the same place in the sky as well as their clustering. Comparison of the model results for different types of lightning discharges indicates that positive cloud to ground discharges lead to the largest electric fields and optical emissions at ionospheric altitudes since they are associated with the removal of larger amounts of charge from higher altitudes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/96JA03528

Sprites produced by quasi-electrostatic heating and ionization in the lower ionosphere

The physics of lightning

With an instantaneous view of 70% of the sky, the Fermi Gamma-ray Burst Monitor (GBM) is an excellent partner in the search for electromagnetic counterparts to gravitational-wave (GW) events. GBM observations at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914 reveal the presence of a weak transient above 50 keV, 0.4 s after the GW event, with a false-alarm probability of 0.0022 (2.9(sigma)). This weak transient lasting 1 s was not detected by any other instrument and does not appear to be connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. Its localization is ill-constrained but consistent with the direction of GW150914. The duration and spectrum of the transient event are consistent with a weak short gamma-ray burst (GRB) arriving at a large angle to the direction in which Fermi was pointing where the GBM detector response is not optimal. If the GBM transient is associated with GW150914, then this electromagnetic signal from a stellar mass black hole binary merger is unexpected. We calculate a luminosity in hard X-ray emission between 1 keV and 10 MeV of 1.8(sup +1.5, sub -1.0) x 10(exp 49) erg/s. Future joint observations of GW events by LIGO/Virgo and Fermi GBM could reveal whether the weak transient reported here is a plausible counterpart to GW150914 or a chance coincidence, and will further probe the connection between compact binary mergers and short GRBs.

/pdf/fermi-gbm-observations-of-ligo-gravitational-wave-event-4vj9ppzxmp.pdf

Fermi GBM Observations of LIGO Gravitational Wave event GW150914

Abstract Geomagnetic disturbances have affected electrical systems on the ground for over 150 years. The first effects were noted on the early telegraph in the 1840s and in this century magnetic storms have caused power system blackouts and phone system outages. Affected systems include all those that use electrical conductors: whether for transmission of power or signals or where the conducting properties are incidental to their use such as with pipelines and railway tracks. In power systems geomagnetically induced currents cause partial saturation of power transformers producing transformer heating and distortion of the ac waveform leading to misoperation of relays and other equipment. On pipelines, induced currents may contribute to corrosion but also present a problem with the electrical surveys of the pipe performed to monitor the corrosion prevention systems. Severity of these effects depends on disturbance size, proximity to the auroral zone, and the conductivity structure of the Earth. Also significant are system parameters such as the use of higher resistance coatings on pipelines and the linking of power systems into larger networks. In this paper we have attempted to catalogue all the published reports of geomagnetic effects on electrical systems and show their occurrence in the context of the solar cycle and geomagnetic activity variations for the years 1844 to 1996.

The Effects of Geomagnetic Disturbances on Electrical Systems at the Earth's Surface - An Update

http://wwlln.net/publications/dowden.toga.article.pdf

VLF lightning location by time of group arrival (TOGA) at multiple sites

. An experimental Very Low Frequency (VLF) World-Wide Lightning Location Network (WWLLN) has been developed through collaborations with research institutions across the world, providing global real-time locations of lightning discharges. As of April 2006, the network included 25 stations providing coverage for much of the Earth. In this paper we examine the detection efficiency of the WWLLN by comparing the locations from this network with lightning location data purchased from a commercial lightning location network operating in New Zealand. Our analysis confirms that WWLLN favours high peak current return stroke lightning discharges, and that discharges with larger currents are observed by more stations across the global network. We then construct a first principles detection efficiency model to describe the WWLLN, combining calibration information for each station with theoretical modelling to describe the expected amplitudes of the VLF sferics observed by the network. This detection efficiency model allows the prediction of the global variation in WWLLN lightning detection, and an estimate of the minimum CG return stroke peak current required to trigger the network. There are strong spatial variations across the globe, primarily due to station density and sensitivity. The WWLLN is currently best suited to study the occurrence and impacts of high peak-current lightning. For example, in 2005 about 12% of the global elve-producing lightning will have been located by the network. Since the lightning-EMP which produce elves has a high mean rate (210 per minute) it has the potential to significantly influence the ionosphere on regional scales.

https://angeo.copernicus.org/articles/24/3197/2006/angeo-24-3197-2006.pdf

Detection efficiency of the VLF World-Wide Lightning Location Network (WWLLN): initial case study

[1] Using the detected energy per strokes of the World Wide Lightning Location Network (WWLLN) we calculate the relative detection efficiency for the network as if it had a uniform detection efficiency. The model uses the energy statistics of located strokes to determine which stations are sensitive to what stroke energies. We are then able to estimate the number of strokes that may be missing from any given regions as compared to the best, most sensitive regions of the WWLLN network. Stroke density maps can be corrected with the knowledge of how sensitive various regions of the network are operating. This new model for the relative WWLLN detection efficiency compensates for the uneven global coverage of the network sensors as well as variations in very low frequency (VLF) propagation. The model gives a way to represent the global distribution of strokes as if observed by a globally uniform network. The model results are analyzed in spatial and temporal regimes, and the effects of a single VLF detector going offline are investigated in areas of sparse and dense detector coverage. The results are also used to show spatial, temporal and energy distributions as seen by the detection efficiency corrected WWLLN.

/pdf/relative-detection-efficiency-of-the-world-wide-lightning-2lj1g5lw3f.pdf

Relative detection efficiency of the World Wide Lightning Location Network

 An experimental VLF World-Wide Lightning Location (WWLL) network has been developed through collaborations with research institutions across the globe The aim of the WWLL is to provide global real-time locations of lightning discharges, with >50% CG flash detection efficiency and mean location accuracy of The detection efficiency of the WWLL is also considered In the selected region the WWLL detected ~13% of the total lightning, suggesting a ~26% CG detection efficiency and a ~10% IC detection efficiency Based on a comparison between all WWLL good lightning locations in February-April 2004, and the activity levels expected from satellite observations we estimate that the WWLL is currently detecting ~2% of the global total lightning, providing good locations for ~5% of global CG activity The existing WWLL network is capable of providing real-time positions of global thunderstorm locations in its current form

/pdf/location-accuracy-of-vlf-world-wide-lightning-location-wwll-43me5b2jsj.pdf

Location accuracy of VLF World-Wide Lightning Location (WWLL) network: Post-algorithm upgrade

An experimental Very Low Frequency (VLF) World‐Wide Lightning Location Network (WWLLN) is being developed through collaborations with research institutions across the globe In this paper we report on the steady improvement in the Detection Efficiency (DE) of the WWLLN due to increasing station number, which led to a doubling in locations provided from 2003–2007 In addition, a new algorithm has recently been implemented which leads to DE improvements of 63%

James B. Brundell

Papers

VLF lightning location by time of group arrival (TOGA) at multiple sites

Detection efficiency of the VLF World-Wide Lightning Location Network (WWLLN): initial case study

Relative detection efficiency of the World Wide Lightning Location Network

Location accuracy of VLF World-Wide Lightning Location (WWLL) network: Post-algorithm upgrade

Growing Detection Efficiency of the World Wide Lightning Location Network