Wide Lightning Location Network Data Research Articles

VLF and Ionospheric D‐Region Perturbations Associated With WWLLN‐Detected Lightning in the South Pacific Region

AbstractThe subionospheric early very low frequency (VLF) perturbations observed on NWC (19.8 kHz) navigational transmitter signal monitored at a low‐latitude station, Suva (18.1°S, 178.5°E), Fiji, during campaign periods of November 2011, 2012, and 2014 and December 2014, are presented. Early VLF events are associated with D‐region conductivity changes mainly produced by lightning‐generated transient luminous events (TLEs). Early VLF events occurred both during daytime and nighttime, with a considerably higher occurrence at nighttime. VLF perturbations caused by lightning strokes located up to 100 km off the transmitter‐receiver great circle path (TRGCP) are attributed to narrow‐angle scattering, while lightning strokes 100–500 km off the TRGCP are considered to cause early VLF events by wide‐angle scattering. Using the World Wide Lightning Location Network data, for the first time, we have studied the relationship between the energy of lightning strokes and the level of VLF perturbations. Greater is the energy of lightning, greater would be the strength of the VLF perturbation. However, the low‐energy lightning stroke can also produce a comparable level of perturbation to that of strong lightning. The modeling results of scattered amplitude (M) and echo phase (ϕE) of the unusually long recovery early/fast VLF event showed a better exponential fit (r ∼ 0.9) than the logarithmic fit. Long‐wavelength propagation capability (LWPC) code modeling of nighttime early VLF events considering causative TLE width of 50 km column indicated a decrease in the D‐region reference height (Hʹ) by up to 30 km and an increase in the sharpness factor (β) by 0.25 km−1.

Significantly Increased Lightning Activity Over the Tibetan Plateau and Its Relation to Thunderstorm Genesis

AbstractUnder the context of global warming, we identified a significant increase in lightning activity in the last two decades over the Tibetan Plateau (TP), the highest plateau on earth, based on two data sets. The largest rise of lightning activity was found over the region with high lightning density represented by the eastern TP at a rate of 0.072 ± 0.069 fl km−2 yr−1 during 1996–2013 from Optical Transient Detector/Lightning Imaging Sensor. World Wide Lightning Location Network data also showed a remarkable increase in lightning strokes during 2010–2019 in the maximum lightning density region, while the change was insignificant in the low lightning density region. Further investigations revealed that most of the TP region experienced a significant increase in thunderstorm frequency, which was responsible for the increase in lightning activity, rather than an increase in thunderstorm intensity. Increased lightning activity implies a potential risk to human beings and the fragile ecosystem over the TP in a warmer climate.

Lightning activity in northern Europe during a stormy winter: disruptions of weather patterns originating in global climate phenomena

Abstract. In this study, we use World Wide Lightning Location Network data and investigate properties of more than 90 000 lightning strokes which hit northern Europe during an unusually stormy winter in 2014/15. Thunderstorm days with at least two strokes hitting an area of 0.5∘ × 0.5∘ occurred 5–13 times per month in the stormiest regions. Such frequency of thunderstorm days is about 5 times higher than the mean annual number calculated for the same region over winter months in 2008–2017. The number of individual winter lightning strokes was about 4 times larger than the long-term median calculated over the last decade. In the colder months of December, January and February, the mean energy of detected strokes was 2 orders of magnitude larger than the global mean stroke energy of 1 kJ. We show for the first time that winter superbolts with radiated electromagnetic energies above 1 MJ appeared at night and in the morning hours, while the diurnal distribution of all detected lightning was nearly uniform. We also show that the superbolts were often single stroke flashes and that their subsequent strokes never reached megajoule energies. The lightning strokes were concentrated above the ocean close to the western coastal areas. All these lightning characteristics presume anomalously efficient winter thundercloud charging in the eastern North Atlantic, especially at the sea–land boundary. We found that the resulting unusual production of lightning could not be explained solely by an anomalously warm sea surface caused by a positive phase of the North Atlantic Oscillation and by a starting super El Niño event. Increased updraft strengths, which are believed to accompany the cold-to-warm transition phase of El Niño, might have acted as another charging driver. We speculate that a combination of both these large-scale climatic events might have been needed to produce the observed enormous amount of winter lightning in winter 2014/15.

WWLLN Hot and Cold-Spots of Lightning Activity and Their Relation to Climate in an Extended Central America Region 2012–2020

Lightning activity has been recognized to have, historically, social and environmental consequences around the globe. This work analyzes the space-time distribution of lightning-densities (D) in an extended Central America region (ECA). World Wide Lightning Location Network data was analyzed to link D with dominant climate patterns over the ECA for 2012–2020. D associated with cold surges entering the tropics dominate during boreal winter. The highest D (hot-spots) was found to agree well with previously known sites, such as the “Catatumbo” in Venezuela; however, D was lower here due to different detection efficiencies. Previously reported hot-spots showed strong continental signals in CA; however, in this work, they were over the oceans near to coastlines, especially in the eastern tropical Pacific (ETP). Most cold-spots, implying a minimum of vulnerability to human impacts and to some industries, were situated in the Caribbean Sea side of Central America. The Mid-Summer-Drought and the Caribbean-Low-Level-Jet (CLLJ) markedly reduced the D during July-August. The CLLJ in the central CS and across the Yucatan and the southern Gulf of Mexico acts as a lid inhibiting convection due to its strong vertical shear during the boreal summer. The CLLJ vertical wind-shear and its extension to the Gulf of Papagayo also diminished convection and considerably decreased the D over a region extending westward into the ETP for at least 400–450 km. A simple physical mechanism to account for the coupling between the CLLJ, the MSD, and lightning activity is proposed for the latter region.

Multi‐Point Observation of Hiss Emerging From Lightning Whistlers

AbstractWe analyze continuous multi‐point measurements of electromagnetic field waveforms onboard the Cluster spacecraft in order to contribute to the discussion on sources of plasmaspheric hiss, known as a shaping agent for the Earth radiation belts. In our case study we aim at finding sources of hiss observed close to the geomagnetic equator in the outer plasmasphere on the dayside. We find hiss to be triggered from whistlers of different spectral properties. Whistlers with the lowest observed dispersion arrive to different spacecraft with time delays indicating their origin in the northern hemisphere. Positions of source lightning discharges are then found using the time coincidences with the Word Wide Lightning Location Network data from three active thunderstorm regions in Europe. We find that subionospheric propagation of lightning atmospherics is necessary to explain the observations. Geographic locations of their ionospheric exit points then determine spectral properties of resulting unducted whistlers and triggered hiss. By this well documented chain of events starting with a lightning discharge in the atmosphere we confirm that magnetospherically reflecting whistlers and hiss triggered from them are among possible sources of plasmaspheric hiss.

The First Terrestrial Electron Beam Observed by the Atmosphere‐Space Interactions Monitor

AbstractWe report the first Terrestrial Electron Beam detected by the Atmosphere‐Space Interactions Monitor. It happened on 16 September 2018. The Atmosphere‐Space Interactions Monitor Modular X and Gamma ray Sensor recorded a 2 ms long event, with a softer spectrum than typically recorded for Terrestrial Gamma ray Flashes (TGFs). The lightning discharge associated to this event was found in the World Wide Lightning Location Network data, close to the northern footpoint of the magnetic field line that intercepts the International Space Station location. Imaging from a GOES‐R geostationary satellite shows that the source TGF was produced close to an overshooting top of a thunderstorm. Monte‐Carlo simulations were performed to reproduce the observed light curve and energy spectrum. The event can be explained by the secondary electrons and positrons produced by the TGF (i.e., the Terrestrial Electron Beam), even if about 3.5% to 10% of the detected counts may be due to direct TGF photons. A source TGF with a Gaussian angular distribution with standard deviation between 20.6° and 29.8° was found to reproduce the measurement. Assuming an isotropic angular distribution within a cone, compatible half angles are between 30.6° and 41.9°, in agreement with previous studies. The number of required photons for the source TGF could be estimated for various assumption of the source (altitude of production and angular distribution) and is estimated between 1017.2 and 1018.9 photons, that is, compatible with the current consensus.

Characteristics of Typhoon Eyewalls According to World Wide Lightning Location Network Data

Abstract Methods for the estimation of typhoon eyewall characteristics (the center location, the radius and the width, and radii of inner and outer boundaries) based on World Wide Lightning Location Network (WWLLN) data are presented and discussed in this work. The center locations, the eyewall radii, and inner boundary radii estimated from WWLLN data for the typhoons of the northwestern Pacific from 2011 to 2015 were compared with the typhoon centers, radii of maximum winds, and the radii of the eyes obtained from Advanced Scatterometer (ASCAT) wind data, the Japan Meteorological Agency (JMA) archives, and the Joint Typhoon Warning Center (JTWC) archives. It is shown that the eyewall characteristics estimates based on the lightning discharge data are most closely related to characteristics of the ASCAT wind speed fields, and the radii of the eyewalls and their inner boundaries are linearly related to the radii of maximum winds and the radii of the eyes, with correlation coefficients reaching approximately 0.9 and 0.8, respectively. It was shown that the distances between locations of the eyewalls and typhoon centers estimated according to the WWLLN and those of the ASCAT, JMA, and JTWC data on average were 19, 16, and 17 km, respectively. The eyewall widths varied from 15 to 69 km, with an average of ~30 km.

Observationally Weak TGFs in the RHESSI Data.

Terrestrial gamma ray flashes (TGFs) are sub‐millisecond bursts of high energetic gamma radiation associated with intracloud flashes in thunderstorms. In this paper we use the simultaneity of lightning detections by World Wide Lightning Location Network to find TGFs in the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) data that are too faint to be identified by standard search algorithms. A similar approach has been used in an earlier paper, but here we expand the data set to include all years of RHESSI + World Wide Lightning Location Network data and show that there is a population of observationally weak TGFs all the way down to 0.22 of the RHESSI detection threshold (three counts in the detector). One should note that the majority of these are “normal” TGFs that are produced further away from the subsatellite point (and experience a 1/r 2 effect) or produced at higher latitudes with a lower tropoause and thus experience increased atmospheric attenuation. This supports the idea that the TGF production rate is higher than currently reported. We also show that compared to lightning flashes, TGFs are more partial to ocean and coastal regions than over land.

Fields of Lightning Discharges in Typhoons

We report the results of the use of the World Wide Lightning Location Network data to analyze the core structure of super typhoons that occurred in the northwestern Pacific Ocean in 2012–2013. The distributions of lightning discharges are compared to the ocean-surface wind fields according to the data of the Advanced Scatterometer (ASCAT) and the infrared images of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the MetTop-A and Aqua satellites, respectively. In the central regions of all of the studied typhoons, the structures that are fragments of circular or spiral mesometeorological-scale forms, which can be related to the presence of the cloud eyewall of typhoons, are observed even a day before the typhoon’s maximum intensity. These circular structures become completely apparent on the day of the typhoon’s maximum intensity and then begin to break down. It is shown that the position of the center of a typhoon and its traveling speed can be estimated from the distribution of lightning; in addition, the geometric characteristics of an eyewall, which are listed in reports on storms and typhoons, can be determined.

Subionospheric VLF perturbations observed at a low latitude station Varanasi (L = 1.07)

Initial results of subionospheric very low frequency (VLF) perturbations observed on NWC (19.8kHz) and NPM (21.4kHz) transmitter signals at low latitude ground station Varanasi, India, during the period January–June 2010, are presented. Characteristics and occurrence rates of these events mainly observed during nighttime are studied. Most of the early VLF events had slow recovery with amplitude perturbations of 0.5–4.5dB and phase changes of 3–12°. Temporal variation of the events is studied. World Wide Lightning Location Network data along with the broadband VLF data are analyzed to find the location of causative lightning discharge and/or the sferics associated with these early VLF events. Lightning induced changes in D-region ionospheric conductivity are attributed to the perturbations in the VLF signals.

Climatology of precipitation and lightning over the Pacific coast of southern Mexico retrieved from Tropical Rainfall Measuring Mission satellite products and World Wide Lightning Location Network data

Tropical Rainfall Measuring Mission (TRMM) satellite products for the period 1998–2009 are used to elaborate the climatology of vertical hydrometeor profiles and diurnal evolution of rainfall over the Pacific coast of southern Mexico. Precipitation characteristics are compared with those of lightning strokes, registered by the World Wide Lightning Location Network (WWLLN). The WWLLN data are verified against a climatological product (High-Resolution Monthly Climatology, HRMC) obtained from merged data sets of the TRMM Lightning Imaging Sensor (LIS) and the Optical Transient Detector (OTD) of the MicroLab-1 satellite. The TRMM 2A12 data set reveals that summer precipitation over the study region is a result of mixed phase processes, whereas during winter and spring, there is a significant contribution of warm precipitation over land. Diurnal evolution of rainfall retrieved from the 3B42 TRMM product and lightning registered by the WWLLN follows the sea–land breeze cycle measured by Baumgardner et al. (2006; Evolution of anthropogenic aerosols in the coastal town of Salina Cruz, Mexico: part I particle dynamics and land–sea interactions, Science of the Total Environment, 367, pp. 288–301). The spatial distribution of lightning is similar to that of rainfall; however, over the seaside coastal region, a phase shift is observed between these two variables, with the maximum lightning activity occurring about 3 hours before the precipitation peak. Monthly distribution of flashes is monomodal over land and bimodal over the ocean. Over the ocean, the evolution of monthly rainfall during summer is contrary to that of lightning activity: the months with highest precipitation (June and September) correspond to those with the lowest number of lightning strokes, whereas during the mid-summer drought, an increase in electrical activity is observed. An explanation for this phenomenon, related to the wind circulation and its effect on the concentration of aerosol particles, is proposed.

D-region ionosphere response to the total solar eclipse of 22 July 2009 deduced from ELF-VLF tweek observations in the Indian sector

[1] Observations of tweeks with higher harmonics (n > 1) at low latitude stations Allahabad and Nainital, in the Indian sector, during the total solar eclipse on 22 July 2009, are presented. Allahabad and Nainital stations were in 100% and 85% of the totality paths. Observations suggest that about 30–40% obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in nighttime. A total of 148 tweeks at Allahabad and 20 tweeks at Nainital were recorded with some of them up to 3rd harmonics. The World Wide Lightning Location Network data indicated that tweeks observed were generated by lightning's located in the partial eclipse area of Asia-Oceania region. The changes in D-region ionospheric VLF reflection height and electron density (∼22–23 cm−3) during eclipse have been estimated from the first cut-off frequency of the tweeks. The reflection height increased from ∼89 km from the first occurrence of tweek to about 91–92 km at the totality and then decreased to ∼87 km at the end of the eclipse, suggesting a change of about 5 km in the reflection height during eclipse. The reflection heights are lower by 2–3 km as compared to normal nighttime tweek reflection heights. The above increase in the reflection height indicate that the partial nighttime condition is created during eclipse, as the main D-region ionizing radiation Lyman α is blocked but solar soft X-ray and EUV radiations originating from the limb solar corona are not totally blocked which produce some of ionization in the D-region.

Improvement in lightning geolocation by time-of-arrival method using global ELF network data

[1] The global observation of cloud-to-ground (CG) discharges based on ELF measurements provides essential information, including vertical charge moment (Qdl) for investigations of global-scale thunderstorm activity. However, the geolocating method by direction finding of sferics in the frequency range of 1–100 Hz has a rather large error, on the order of 1000 km, even for the CGs with relatively large Qdl (>1000 C-km). Here we improve the methods for geolocation and estimation of Qdl, which are applicable to smaller CGs with Qdl down to 470 C-km, making use of the time-of-arrival method and the high correlation between Qdl and the peak amplitude of ELF sferics. The evaluated average error in geolocation, comparing with World Wide Lightning Location Network data, is 680 km. By this improved method, CGs with Qdl of <470 C-km can be detected at any location in the world. In the preliminary analysis for the year of 2004, the number of CGs whose location and Qdl are determined is about a million events per month, roughly 10–30 times compared to previous studies by ELF measurement, enabling an investigation of the day-to-day variations of the global CG distribution with transferred charge amount. The combination of accurate geolocation and the uniformity of detection show active regions in the three main areas: Africa, South America, and the Maritime Continent. In addition, minor thunderstorm areas in Japan, the Mediterranean Sea, and the Pacific Ocean can be monitored.