Parent Lightning Discharges Research Articles

Low-frequency (ELF�VLF) radio atmospherics study at the Ukrainian Antarctic Akademik Vernadsky station

This paper describes the results of the atmospherics measurements in the extremely low-frequency (ELF) and very low-frequency (VLF) frequency ranges performed at the Akademik Vernadsky station (64.26W; 65.25S) during February–April 2019. The main objective of the study was the implementation of a single-site technique for monitoring the lower ionosphere parameters and locating globally distributed powerful lightning discharges. Methods. The receiving and analyzing VLF complex was used at the station to record two horizontal magnetic and vertical electric components of atmospherics in the frequency range 750 Hz – 24 kHz. A single-site lightning location method is based on the analysis of tweek-atmospherics (tweeks).It was implemented in the receiving system software. This allowed obtaining real-time information about lightning position, height and electron density variations in the lower ionosphere.The records of VLF atmospherics were synchronized via GPS timestamps with records of ELF transients resulted from globally distributed powerful lightning discharges. Results of analysis of tweeks recorded at the Akademik Vernadsky station indicates that lightning discharges are registered at distances from 2,000 km to about 10,000 km within the azimuthal sector, covering almost the entire South American continent, southern Africa and the Gulf of Guinea. Practically, no tweeks from the Pacific were recorded. This can be attributed to the non-reciprocity of attenuation of radio waves propagating in the west-east and east-west directions. In addition to the fundamental mode, we observed also the second and higher order modes of tweeks. This allowed estimating the lower boundary altitude and the electron density in the lower ionosphere. We demonstrated the advantages of simultaneous recordings of VLF atmospherics and ELF transients. Employing the vertical electric and two horizontal magnetic components measured by the VLF complex allowed for more accurate and unambiguous determining the source azimuth and resolving polarity of the charge transfer in the parent lightning discharges. Combining the ELF and VLF records, we can determine a distance to lightning and, then, parameters of the current moment of the lightning discharge. Conclusions. The performed experimental studies has shown the prospect of further combined ELF–VLF monitoring at the Akademik Vernadsky station, enabling detection of globally distributed powerful lightning discharges and changes in the lower ionosphere related to various phenomena of space weather, atmospheric and of terrestrial origin.

Charge moment change and lightning‐driven electric fields associated with negative sprites and halos

Sprites are structured high altitude optical emissions produced by lightning‐driven electric fields. Both strong positive and negative cloud to ground flashes (CGs) are capable of initiating sprites. However, reported sprites are almost exclusively produced by +CGs. The very limited number of negative polarity sprites makes it difficult to reveal their morphologies and mechanisms. Since 2008, we have operated low light cameras at 5 locations in the United States to detect lightning‐driven transient luminous events (TLEs). At Duke University, two pairs of magnetic sensors simultaneously record lightning‐radiated magnetic fields. During 4 years of observations, the low light cameras collectively captured 1651 sprite events. Among them, 6 were produced by −CG lightning, which was confirmed by both the National Lightning Detection Network (NLDN) and magnetic field measurements. All of these negative sprites show similar features in their morphology, lightning source current, and lightning‐driven ambient electric fields. They all initiate within a few ms from their parent lightning discharges and always are accompanied by sprite halos. Compared to positive sprites, the downward streamers in negative sprites terminate at higher altitudes, about 55–60 km. The extracted source current of their parent lightning discharges is very impulsive and produces at least 450 C km charge moment change in 0.5 ms or less. Unlike most +CG strokes, essentially no continuing current follows these −CGs. Thus the uniformity of negative sprite morphology appears to reflect the uniformity of the characteristics of high charge transfer negative strokes. Numerical simulation shows these impulsive source currents produce very high (>2 Ek, where Ek is the local air breakdown field) but short‐lived electric fields at halo altitudes between 70 km and 90 km. At streamer termination altitudes, the inferred background electric field is 0.2–0.3 Ek, which is close to but below the critical field (0.4 Ek) for negative streamer propagation. The simulations also show that the timescale of the lightning source current has a significant impact on the high altitude electric fields and thus the sprite initiation and morphology. With the same amount of charge transfer, a more impulsive current source produces a higher electric field of shorter duration at halo and sprite altitudes. The short timescales may explain why a larger threshold of total charge moment change is required to initiate negative sprites than short‐delayed positive sprites, whose parent lightning source current is usually less impulsive.

The Global Lightning and Sprite Measurement (GLIMS) Mission on International Space Station -Concept and Overview-

Global Lightning and sprIte MeasurementS (GLIMS) is a mission on the International Space Station (ISS) to detect and locate optical transient luminous events (TLEs) and associated lightning simultaneously from the non-sun-synchronous orbit. It is scheduled to be launched from Japan in January, 2012 as part of the multi-mission consolidated equipment on the Japanese Exposure Module (JEM). Our mission's goals are (1) to detect and locate lightning and sprites within storm scale resolution over a large region of the Earth's surface along the orbital track of the ISS without any bias, (2) to clarify the mechanism by which sprites are generated, and (3) to identify the conditions under which TLEs occur. To achieve these goals, two CMOS cameras, six Photometers, a VLF receiver and VHF interferometer with two antennas are installed at the bottom of the module to observe the TLEs, as well as causative lightning discharges at nadir direction during day and night time. Though the luminous events' so-called sprites, elves and jets have been investigated by numerous researchers all over the world based mainly on ground observations, some important problems have not been fully understood yet. These include the generation mechanisms of columniform fine structures and horizontal offset of some sprites from the parent lightning discharges. In the JEM-GLIMS mission, observations from our synchronized sensors will shed light on the unsolved problems mentioned above regarding TLEs and causative lightning discharges. In this presentation scientific background, instrumentation, and project summaries are given.

Lightning and Sprite Observation from International Space Station

Lightning and sprite measurement sensors on the International Space Station (ISS) are introduced in this paper. Lightning is an electrical discharge which neutralizes the charge inside thunderstorm. In the early 1990s, optical transient luminous events (TLEs) occurring just above the thunderstorm were firstly reported by the US scientists and are associated with positive cloud-to-ground discharges with a large amount of charge. Though the luminous events so-called sprite, elves and jets have been investigated by numerous researchers all over the world based mainly on the ground observations, some important problems have not been fully understood yet such as generation mechanisms of columniform fine structure and horizontal offset of some sprites from the parent lightning discharges. In the JEM-GLIMS mission, observations from our synchronized sensors are going to shed light on above-mentioned unsolved problems regarding TLEs as well as causative lighting discharges. Our goals are (1) to detect and locate lightning and sprite within storm scale resolution over a large region of the Earth's surface along the orbital track of the ISS without any bias, (2) to clarify the generation mechanism of sprite, and (3) to identify the occurrence conditions of TLEs.

Six-Channel Spectrophotometers (PH) Onboard JEM-GLIMS

Six-channel spectrophotometers (PH) are the science instruments of JEM-GLIMS to measure absolute intensity of the emission originated from lightning discharges and upper atmospheric transient luminous events (TLEs). PH unit-1 (PH-U1) consists of four spectrophotometer channels named from PH1 to PH4, while PH unit-2 (PH-U2) two spectrophotometer channels named PH5 and PH6. Optical filters of these spectrophotometers are selected to detect TLE emission lines of N2 1PG, N2 2PG, N2+ 1NG, and N2 LBH. Since the bandwidth of the optical filter of PH2, 3, 5, and 6 is 10 nm and since PH1 measures NUV emission, photomultiplier tubes with high-voltage converters are used as a photon detector. To the contrary, PH4 uses a photodiode as a photon detector because the pass-band of the optical filter is enough wide to detect transient optical emission. Though PH does not equip spatial resolution, it can acquire light curve data with a high time resolution of 50 μs with a 12-bit resolution. Thus, the combinational analysis of PH data and Lightning and Sprite Imager (LSI) data, it is possible to clarify the relationship between TLEs and their parent lightning discharges, the occurrence condition of TLEs, and the energy of the electrons which excite TLE emission.

A comparison of different source location methods for ELF transients by using the parent lightning discharges with known positions

Different kinds of direction finding methods (azimuth and range determinations) have been proposed so far in order to locate ELF transients. As for the azimuth determination, we have used the Lissajous method and goniometer and Poynting vector methods, which are found to be not so much different. The biggest problem is the range (or source‐to‐observer distance) estimation, which is principally based on the use of wave impedance. By using the known positions of parent lightning discharges during the European sprite campaign, we have compared different methods ((1) cross‐correlation over a wide frequency range between the measured and theoretical wave impedances, (2) the use of peak frequency in the observed wave impedance, (3) Jones and Kemp method (the use of maxima and minima in the frequency spectrum of wave impedance), (4) the use of oscillation frequency in the wave impedance variation), and it is found that the best one is the use of Jones and Kemp method with an error of 0.33 Mm for the nine events with sufficient S/N ratio from the analyzed 11 events. This has been based on the FFT analysis. However, for the remaining two events with small time separation, we have tried the use of wavelet analysis, which improved the range determination significantly. Finally, we recommend a combined use of Jones and Kemp method and wavelet analysis for locating ELF transients.

A survey of ELF and VLF research on lightning‐ionosphere interactions and causative discharges

Extremely low frequency (ELF) and very low frequency (VLF) observations have formed the cornerstone of measurement and interpretation of effects of lightning discharges on the overlying upper atmospheric regions, as well as near‐Earth space. ELF (0.3–3 kHz) and VLF (3–30 kHz) wave energy released by lightning discharges is often the agent of modification of the lower ionospheric medium that results in the conductivity changes and the excitation of optical emissions that constitute transient luminous events (TLEs). In addition, the resultant ionospheric changes are best (and often uniquely) observable as perturbations of subionospherically propagating VLF signals. In fact, some of the earliest evidence for direct disturbances of the lower ionosphere in association with lightning discharges was obtained in the course of the study of such VLF perturbations. Measurements of the detailed ELF and VLF waveforms of parent lightning discharges that produce TLEs and terrestrial gamma ray flashes (TGFs) have also been very fruitful, often revealing properties of such discharges that maximize ionospheric effects, such as generation of intense electromagnetic pulses (EMPs) or removal of large quantities of charge. In this paper, we provide a review of the development of ELF and VLF measurements, both from a historical point of view and from the point of view of their relationship to optical and other observations of ionospheric effects of lightning discharges.

On remote sensing of transient luminous events' parent lightning discharges by ELF/VLF wave measurements on board a satellite

First recordings of satellite ELF/VLF waveform data associated with transient luminous event (TLE) observations are reported from the summer 2005 campaign coordinated by Stanford University and Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPCE). TLEs are optically observed from the U.S. Langmuir Laboratory, while ELF/VLF waveform data are simultaneously recorded on board the Centre National d'Etudes Spatiales microsatellite DEMETER and on the ground at Langmuir. Analyses of ELF/VLF measurements associated with sprite events observed on 28 July 2005 and 3 August 2005 are presented. Conditions to trace back the wave emissions from the satellite to the source region of the parent lightning discharge are discussed. The main results concern: (1) the identification from a low Earth orbit satellite of the 0+ whistler signatures of the TLE causative lightning; (2) the identification of the propagation characteristics of proton whistlers triggered by the 0+ whistlers of the causative lightning, and the potential use of those characteristics; (3) recognition of the difficulty to observe sprite‐produced ELF bursts in the presence of proton‐whistlers; (4) the use of geographical displays of the average power received by the DEMETER electric field antennas over the U.S. Navy transmitter North West Cape (NWC) located in Western Australia to evaluate VLF transmission cones which explain the presence (28 July events) or the absence (3 August events) of propagation links between sferics observed at ground and 0+ whistlers observed on DEMETER; and (5) owing to electron‐collisions, an optimum transfer of energy from the atmosphere to the ionosphere for waves with k vectors antiparallel, or quasi‐antiparallel, to Earth's magnetic field direction.

ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign

During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3–3000 Hz) and broadband very low frequency (VLF: 3–30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites. The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm-activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods. Additionally, more than one +CG was associated with six of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements.

Comparison of time delays of sprites induced by winter lightning flashes in the Japan Sea with those in the Pacific Ocean

The measurement of unusual winter sprites in the Hokuriku area (Japan Sea side) was performed as a primary target of the 2006/2007 winter campaign by means of coordinated optical and extremely low frequency (ELF)/very high-frequency (VHF) electromagnetic observations. We have also added the same observations for the sprites in the Pacific Ocean, to be compared with the characteristics of Hokuriku sprites. The following results have emerged from this campaign: (i) the predominance of column sprites in winter has been confirmed not only for the Hokuriku area but also in the Pacific Ocean (with the probability just above 60%), (ii) carrots are much more frequently observed in the Pacific Ocean (with a probability of ∼28%) than in the Hokuriku area (∼16%), (iii) a very unique property of Hokuriku sprites is the surprisingly long delay (average ∼90 ms) of sprites from their parent lightning flashes and the delays for carrots and columns exhibit some significant difference (80 ms for columns and 100 ms for carrots) and (iv) the time delay of Pacific Ocean sprites is much shorter (∼43 ms average) than that at Hokuriku, but there is no remarkable difference in delay between carrots and columns. Finally we discussed the importance of time delay studies to understand sprite generations and their parent lightning discharges, because the difference of time delays on the Japan Sea side and in the Pacific Ocean are thought to be causally related to the parameters of parent thunderstorms.

Testing sprite initiation theory using lightning measurements and modeled electromagnetic fields

Previous research has shown that the statistical measurements of charge moment changes in sprite‐producing lightning are in general agreement with the predictions based on the conventional breakdown theory for sprite initiation in the mesosphere. Measurements have progressed to the point where a detailed, event‐level quantitative comparison between the measurements and predictions could more rigorously test the existing theories by estimating the electric fields above the thunderstorm clouds responsible for sprite initiation. We selected for this analysis a set of sprite events from the summer of 2004 whose initiation times are well bounded. Then we measured the current moments and charge moment changes of the parent lightning discharges using the radiated electromagnetic fields recorded by our extremely low frequency/ultra low frequency lightning remote sensing systems. The measured current moments were then used as the input of a two‐dimensional cylindrical full‐wave finite‐difference time‐domain model for lightning‐generated electromagnetic field simulations. We compared the simulated mesospheric electric fields to the threshold electric field for conventional breakdown to see whether, according to theory, conventional breakdown (and thus a sprite) would be initiated by that electric field and at what altitude. By analyzing sprites that are both short and long delayed from the source lightning strokes, we compared measurements and theory across a wide range of timescales. The results show that for bright, short‐delayed sprites, the measurement‐inferred mesospheric electric field agrees within 20% with the threshold electric field for conventional breakdown. However, for long delayed sprite events and dimmer sprites, the measurement‐inferred mesospheric electric field for sprite initiation is somewhat below the threshold for conventional breakdown.

Characteristics of Japanese winter sprites and their parent lightning as estimated by VHF lightning and ELF transients

Sprites are newly discovered optical emissions in the mesosphere over large thunderstorms. This paper is the observational summary of winter sprites in the Hokuriku area of Japan and their parent lightning in the winter of 2004/2005, by using the coordinated optical and electromagnetic (VHF and ELF) measurements in Japan. As the results of optical observations at two stations, we have found that this campaign has yielded a variety of sprite shapes; V-angle shaped structures have been often observed (25%) in addition to columnar structures familiar for us. All of the sprite events are found to be associated with + CG lightning, as seen from the macroscopic information by ELF data at Moshiri. However, examining the microscopic properties of parent lightning as seen from the VHF SAFIR lightning detection network, has suggested very complicated characteristics of parent lightning discharges inducing sprites, as compared with the ELF data. One half of the sprite events are also found to be associated with + CG by the SAFIR observation, but another half has yielded rather new results as compared with earlier results. Four events are definitely associated with - CG and the remaining three events, inter-cloud flashes. The overall picture for Japanese winter sprites and their parent lightning discharges, is significantly different from that for the summer-time, continental sprites. This is indicative of complexity of winter lightning in the Hokuriku area of Japan and this would provide new information on the sprite generation mechanism.

Characteristics of mesospheric sprites in the Hokuriku area and their causative lightning discharges

AbstractMesospheric optical phenomena (including sprites) are becoming an interesting subject from the standpoint of atmosphere–ionosphere coupling. This paper deals with our observation of sprites associated with winter thunderstorms in the Hokuriku area and we show the characteristics of those sprites and their parent lightning discharges. Although the scale of Japanese lightning in winter is very small compared with the MCS (Mesoscale Convective System) for the summer continental lightning, the essential quantities (polarity, charge transfer, and so on) are found to be nearly the same as those for the MCS. However, an additional factor might be required, such as the self‐organization of the lightning. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 9–17, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20178

Characteristics of Mesopheric Sprites in the Hokuriku Area and their Causative Lightning Discharges

Mesospheric optical phenomena(including sprites) are becoming an interesting subject from the standpoint of atmosphere-ionosphere coupling. This paper deals with our observation of sprites associated with winter thunderstorms in the Hokuriku area and we show the characteristics of those sprites and their parent lightning discharges. Although the scale of Japanese lightning in winter is very small as compared with the MCS (Mesoscale Convective System) for the summer continental lightning, the essential quantities (polarity, charge transfer etc.) are found to be nearly the same as those for those MCS. However, there might be required an additional factor, such as the self-organization of the lightning.