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

. The knowledge of the lightning-induced nitrogen oxides (LNOx) source is important for understanding and predicting the nitrogen oxides and ozone distributions in the troposphere and their trends, the oxidising capacity of the atmosphere, and the lifetime of trace gases destroyed by reactions with OH. This knowledge is further required for the assessment of other important NOx sources, in particular from aviation emissions, the stratosphere, and from surface sources, and for understanding the possible feedback between climate changes and lightning. This paper reviews more than 3 decades of research. The review includes laboratory studies as well as surface, airborne and satellite-based observations of lightning and of NOx and related species in the atmosphere. Relevant data available from measurements in regions with strong LNOx influence are identified, including recent observations at midlatitudes and over tropical continents where most lightning occurs. Various methods to model LNOx at cloud scales or globally are described. Previous estimates are re-evaluated using the global annual mean flash frequency of 44±5 s−1 reported from OTD satellite data. From the review, mainly of airborne measurements near thunderstorms and cloud-resolving models, we conclude that a "typical" thunderstorm flash produces 15 (2–40)×1025 NO molecules per flash, equivalent to 250 mol NOx or 3.5 kg of N mass per flash with uncertainty factor from 0.13 to 2.7. Mainly as a result of global model studies for various LNOx parameterisations tested with related observations, the best estimate of the annual global LNOx nitrogen mass source and its uncertainty range is (5±3) Tg a−1 in this study. In spite of a smaller global flash rate, the best estimate is essentially the same as in some earlier reviews, implying larger flash-specific NOx emissions. The paper estimates the LNOx accuracy required for various applications and lays out strategies for improving estimates in the future. An accuracy of about 1 Tg a−1 or 20%, as necessary in particular for understanding tropical tropospheric chemistry, is still a challenging goal.

/pdf/the-global-lightning-induced-nitrogen-oxides-source-4n884kbcha.pdf

The global lightning-induced nitrogen oxides source

The physics of lightning

[1] Modeling studies indicate that double-headed streamers originating from single electron avalanches in lightning-driven quasi-static electric fields at mesospheric altitudes accelerate and expand, reaching transverse scales from tens to a few hundreds of meters and propagation speeds up to one tenth of the speed of light, in good agreement with recent telescopic, high-speed video and multichannel photometric observations of sprites. The preionization of the medium ahead of a streamer by the ionizing UV photons originating from a region of high electric field in the streamer head (i.e., photoionization) significantly modifies the streamer scaling properties as a function of air pressure in comparison with those predicted by similarity laws. The photoionization leads to lower peak electric fields in the streamer head, lower streamer electron densities, wider initial streamer structures, and lower acceleration and expansion rates of streamers at sprite altitudes 40–90 km, when compared to the ground level. The primary reason for the observed differences is that the effective quenching altitude of the excited states of the molecular nitrogen b1Πu, b′1, and c′41 that give photoionizing radiation is about 24 km. The quenching of these states is therefore negligible at sprite altitudes, leading to a substantial enhancement of the electron-ion pair production ahead of the streamer tip because of the photoionization, when compared to the ground level. The maximum radius of the expanding streamers is predominantly controlled by the combination of the absorption cross section χmin = 3.5 × 10−2 cm−1 Torr−1 of the molecular oxygen (O2) at 1025 A and the partial pressure of O2 in air, Streamers exhibit branching when their radius becomes greater than Model results indicate a lower branching threshold radius for positive streamers in comparison with negative streamers, under otherwise identical ambient conditions. These results are in good agreement with recent results of high-speed photography of laboratory streamers in near-atmospheric pressure N2/O2 mixtures and similar morphology documented during recent telescopic and high-speed video observations of sprites.

/pdf/effects-of-photoionization-on-propagation-and-branching-of-356orhkr3k.pdf

Effects of photoionization on propagation and branching of positive and negative streamers in sprites

Twelve electron-acceleration mechanisms and 10 generator mechanisms for auroral arcs are examined, and a characteristic auroral-arc thickness is worked out for each mechanism except one. The arc thicknesses are then mapped down to the ionosphere along the terrestrial magnetic-field lines; near the Earth, a dipole magnetic-field model is used, and farther from the Earth, the mapping includes the effects of magnetic-field-line draping. The 21 theoretical models all predict auroral-arc thicknesses that are at least an order of magnitude wider than the optically observed arcs. As an alternative explanation of the observed narrow auroral arcs, the acceleration of ionospheric electrons to produce airglow in electrical discharge mechanisms appears improbable. Also unsuccessfully explored is the possibility that the observed narrow auroral arcs are caused by interference effects when Alfven waves reflect off the ionosphere. Suggestions are made for future ground-based auroral-arc measurements.

Auroral arc thicknesses as predicted by various theories

We present three-dimensional simulations of photon transport through clouds, specifically designed to address the characteristics and detection of optical lightning waveforms collected by satellites The model uses a Monte Carlo approach, in which discrete photons are advanced by a standard time step through a distribution of scattering water droplets, whose size and number density distributions are variable The model is different from previous work, in that it considers both finite and infinite cloud geometries and simulates sources of emission with arbitrary spatiotemporal properties The model outputs are designed to be directly comparable to data obtained by the FORTE satellite photodiode detector, which records optical waveforms for lightning events with 15 μs resolution The model treats the light propagation through clouds having a variety of shapes, sizes, and optical depths and constructs the delayed/dispersed/attenuated light curve as seen from arbitrary locations outside of the cloud We compare the simplest case results to previous models and to data from the FORTE satellite and consider certain special cases such as the signal received from impulses occurring below the cloud We find that the shape of the cloud and the position of the event within the cloud, rather than the motion or extent of the event itself, are the greatest determinants of the resultant distribution of photons in the sky We also find that the position of the event within the cloud can be as large a determinant in the apparent attenuation of the signal as the cloud optical depth We find that the class of FORTE optical waveforms with durations ≥1 ms cannot be accounted for by photon scattering alone, but rather, the intrinsic source duration must itself be quite long, which is not the case for return strokes

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JD900051

Simulations of lightning optical waveforms as seen through clouds by satellites

Electrostatic ion‐cyclotron (EIC) waves have been investigated in plasmas containing K+ positive ions, electrons, and SF−6 negative ions Two EIC wave modes are generally present, the K+ and SF−6 modes Their frequencies increase with increasing e, the percentage of negative ions, while the critical electron drift velocities for excitation of either mode decrease with increasing e The observations are discussed on the basis of available theories

Electrostatic ion‐cyclotron waves in a plasma with negative ions

Photometric measurements in the SPRITES ’95 & ’96 campaigns of nitrogen second positive (399.8 nm) and first negative (427.8 nm) emissions

Preliminary observations of simultaneous VHF and optical emissions from lightning as seen by the Fast on-Orbit Recording of Transient Events (FORTE) spacecraft are presented. VHF/optical waveform pairs are routinely collected both as individual lightning events and as sequences of events associated with cloud-to-ground (CG) and intracloud (IC) flashes. CG pulses can be distinguished from IC pulses on the basis of the properties of the VHF and optical waveforms but mostly on the basis of the associated VHF spectrograms. The VHF spectrograms are very similar to previous ground-based HF and VHF observations of lightning and show signatures associated with return strokes, stepped and dart leaders, attachment processes, and intracloud activity. For a typical IC flash, the FORTE-detected VHF is generally characterized by impulsive broadband bursts of emission, and the associated optical emissions are often highly structured. For a typical initial return stroke, the FORTE-detected VHF is generated by the stepped leader, the attachment process, and the actual return stroke. For a typical subsequent return stroke, the FORTE-detected VHF is mainly generated by dart leader processes. The detected optical signal in both return stroke cases is primarily produced by the in-cloud portion of the discharge and lags the arrival of the correspondingmore » VHF emissions at the satellite by a mean value of 243 {mu}s. This delay is composed of a transit time delay (mean of 105 {mu}s) as the return stroke current propagates from the attachment point up into the region of in-cloud activity plus an additional delay due to the scattering of light during its traversal through the clouds. The broadening of the light pulse during its propagation through the clouds is measured and used to infer a mean of this scattering delay of about 138 {mu}s (41 km additional path length) for CG light. This value for the mean scattering delay is consistent with the Thomason and Krider [1982] model for light propagation through clouds. (c) 2000 American Geophysical Union.« less

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JD900993

FORTE observations of simultaneous VHF and optical emissions from lightning: Basic phenomenology

Balloon-borne gamma-ray and electric-field-change instruments were launched into a daytime summer thunderstorm to evaluate a new experimental design to test hypotheses for the production of transient luminous events (TLE) (eg. sprites, and blue jets) in the mesosphere. While ascending, the instrument triggered many times on the signals from the electric-field-change instrument, recording the gamma-ray background at those times. A greater than three-fold increase in the gamma-ray flux was observed as the balloon descended through a thunderstorm anvil where a strong electric field was suspected to be present. These observations suggest that gamma-ray production in thunderstorms may not be as uncommon as previously believed.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999GL010849

David M. Suszcynsky

Papers

Simulations of lightning optical waveforms as seen through clouds by satellites

Electrostatic ion‐cyclotron waves in a plasma with negative ions

Photometric measurements in the SPRITES ’95 & ’96 campaigns of nitrogen second positive (399.8 nm) and first negative (427.8 nm) emissions

FORTE observations of simultaneous VHF and optical emissions from lightning: Basic phenomenology

Gamma-ray emissions observed in a thunderstorm anvil