World Wide Lightning Location Network Research Articles

Characterization of the lightning activity of “Relámpago del Catatumbo”

The “Relámpago del Catatumbo” (Catatumbo Lightning) is a phenomenon known for more than 500 years that occurs in Venezuela. This phenomenon occurs almost all along the year in a very small region of the southwest region of Maracaibo Lake and, according to the Lightning Imaging Sensor (LIS) data, this region presents the highest lightning activity of the world. The region presents a complex topography with particular climatic conditions. The lightning activity of the region was examined using the World Wide Lightning Location Network (WWLLN) data. The results show two very localized high-lightning activity centers: one of them is confined around [9.5°N; 71.5°W] over the southwest region of the Maracaibo Lake, and the other is around [9°N; 73°W] near the Colombia–Venezuela border. The lightning activity has a semiannual behavior with two maxima, one around May and another one around October. The diurnal cycle shows substantial lightning activity during local nights.

Initial Studies with the Lightning Detector on the C/NOFS Satellite, and Cross Validation with WWLLN

Abstract The lightning detector (LD) on the Communications/Navigation Outage Forecast System (C/NOFS) satellite uses a pair of silicon photodiodes, viewing each flank at right angles to the satellite track over an extended field of view. The data product is a report every ½ s of the number of digitizer cycles (125 μs each) for which the detected power was in predefined ranges. The performance of this system over the first 2.5 years of the C/NOFS mission is discussed, statistics of its lightning observations are presented, and a statistical cross validation using the World-Wide Lightning Location Network (WWLLN) as a ground truth is provided. It is found that the LD reports of lightning, despite their blunt timing (½ s), show correlation with strokes detected and located by WWLLN. The irradiance of these strokes lies on the high-power flank of the irradiance distribution seen earlier by the FORTE satellite. Thus, the LD thresholds favor high-power lightning; it is shown that the closest portion of the field of view is more likely to provide WWLLN coincidences than is the furthest portion of the field of view. Statistics of lightning incidence are examined at low latitudes, versus longitude, and distributions that are consistent with those established earlier by the OTD and LIS instruments are retrieved. Finally, the longitude dependence of the irradiance per stroke is examined and the ways in which it differs between the three major lightning “hot spots” is explored. It is observed that the radiance per stroke over the Congo Basin is lower than that over the other two hot spots (Maritime Continent/South Asia and the Americas), consistent with earlier observations by the OTD imager.

Confining the angular distribution of terrestrial gamma ray flash emission

[1] Terrestrial gamma ray flashes (TGFs) are bremsstrahlung emissions from relativistic electrons accelerated in electric fields associated with thunder storms, with photon energies up to at least 40 MeV, which sets the lowest estimate of the total potential of 40 MV. The electric field that produces TGFs will be reflected by the initial angular distribution of the TGF emission. Here we present the first constraints on the TGF emission cone based on accurately geolocated TGFs. The source lightning discharges associated with TGFs detected by RHESSI are determined from the Atmospheric Weather Electromagnetic System for Observation, Modeling, and Education (AWESOME) network and the World Wide Lightning Location Network (WWLLN). The distribution of the observation angles for 106 TGFs are compared to Monte Carlo simulations. We find that TGF emissions within a half angle >30° are consistent with the distributions of observation angle derived from the networks. In addition, 36 events occurring before 2006 are used for spectral analysis. The energy spectra are binned according to observation angle. The result is a significant softening of the TGF energy spectrum for large (>40°) observation angles, which is consistent with a TGF emission half angle (<40°). The softening is due to Compton scattering which reduces the photon energies.

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.

Daily and intraseasonal relationships between lightning and NO2over the Maritime Continent

[1] The relationship between lightning and NO2 over Indonesia is examined on daily and intraseasonal time scales based on lightning observations from the World Wide Lightning Location Network (WWLLN) and tropospheric NO2 column densities from the Global Ozone Monitoring Experiment (GOME‐2) satellite mission. Composites of the daily NO2 observations regressed onto lightning frequency reveal a plume of enhanced NO2 following a day of enhanced lightning. Lightning and NO2 also vary coherently with the intraseasonal Madden‐Julian Oscillation (MJO) in a manner distinct from the cloudiness signature, with variations of up to ∼50% of the annual mean. Citation: Virts, K. S., J. A. Thornton, J. M. Wallace, M. L. Hutchins, R. H. Holzworth, and A. R. Jacobson (2011), Daily and intraseasonal relationships between lightning and NO2 over the Maritime Continent, Geophys. Res. Lett., 38, L19803, doi:10.1029/2011GL048578.

Lightning-generated whistler waves observed by probes on the Communication/Navigation Outage Forecast System satellite at low latitudes

Direct evidence is presented for a causal relationship between lightning and strong electric field transients inside equatorial ionospheric density depletions. In fact, these whistler mode plasma waves may be the dominant electric field signal within such depletions. Optical lightning data from the Communication/Navigation Outage Forecast System (C/NOFS) satellite and global lightning location information from the World Wide Lightning Location Network are presented as independent verification that these electric field transients are caused by lightning. The electric field instrument on C/NOFS routinely measures lightning ]related electric field wave packets or sferics, associated with simultaneous measurements of optical flashes at all altitudes encountered by the satellite (401.867 km). Lightning ]generated whistler waves have abundant access to the topside ionosphere, even close to the magnetic equator.

Study of oblique whistlers in the low-latitude ionosphere, jointly with the C/NOFS satellite and the World-Wide Lightning Location Network

Abstract. We use the C/NOFS satellite's Vector Electric Field Instrument (VEFI) to study the relationship of impulsive electron whistlers in the low-latitude ionosphere to lightning strokes located by the World-Wide Lightning Location Network (WWLLN). In order to systematize this work, we develop an automated algorithm for recognizing and selecting the signatures of electron whistlers amongst many Very Low Frequency (VLF) recordings provided by VEFI. We demonstrate the application of this whistler-detection algorithm to data mining of a ~ two-year archive of VEFI recordings. It is shown that the relatively simple oblique electron whistler adequately accounts of the great majority of low-latitude oscillatory VLF waves seen in this study.

Source region for whistlers detected at Rothera, Antarctica

[1] The accepted mechanism for whistler generation implicitly assumes that the causative lightning stroke occurs within reasonable proximity to the conjugate foot point of the guiding magnetic field line and that nighttime whistlers are prevalent because of low transionospheric attenuation. However, these assumptions are not necessarily valid. In this study we consider whistler observations from Rothera, a station on the Antarctic Peninsula, and contrast their occurrence with global lightning activity from the World Wide Lightning Location Network. The correlation of one-hop whistlers observed at Rothera with global lightning yields a few regions of significant positive correlation. The most probable source region was found over the Gulf Stream, displaced slightly equatorward from the conjugate point. The proximity of the source region to the conjugate point is in accord with the broadly accepted whistler production mechanism. However, there is an unexpected bias toward oceanic lightning rather than the nearby continental lightning. The relationship between the diurnal pattern of the Rothera whistlers and the conjugate lightning exhibits anomalous features which have yet to be resolved: the peak whistler rate occurs when it is daytime at both the source and the receiver and when source lightning activity is at its lowest. As a result, we propose that preferential whistler-wave amplification in the morning sector is a possible cause of the high whistler occurrence, although this does not account for the bias toward oceanic lightning.

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.

Satellite Observations for Lightning Discharges and Analysis of VHF Electromagnetic Waveforms

The Maido-1 satellite observed the lightning discharges from February to October, 2009. We analyzed the observational results with the Maido-1 satellite above Southeast Asia area and the Atlantic Ocean area. First we calculated the change of the pulse width with the electromagnetic wave propagation in the ionosphere. The numerical calculation indicates that the full width at half maximum (FWHM) is changed by the incident angle to the ionosphere. The FWHM increases to tens of nanoseconds through the ionosphere. Next we compared the pulse widths of the received pulses by the Maido-1 satellite in the Atlantic Ocean area and Southeast Asia area. The results in the Atlantic Ocean area have the greater FWHM than those in Southeast Asia area. On the other hand, the results of World Wide Lightning Location Network (WWLLN) indicate that the distance between the position of the radiation source and the observation site in the Atlantic Ocean area is longer than in Southeast Asia area. The calculation results can explain two observational results (the maido-1 satellite and the WWLLN). Then we discussed the relationship between the number of the received pulses and the lightning activity level. From the analysis of the detected number by the WWLLN and the received pulse number by the Maido-1 satellite, the more active the lightning discharges are, the more VHF pulses are radiated.

The World Wide Lightning Location Network and Convective Activity in Tropical Cyclones

Abstract Lightning flash density in tropical cyclones (TCs) is investigated to identify whether lightning flashes provide information on TC intensity and/or intensity change, to provide further insight into TC asymmetric convective structure induced by vertical shear and storm motion, and to assess how well the World Wide Lightning Location Network (WWLLN) is suited for the observation of TCs. The 24 Atlantic basin TCs that came within 400 km of the United States from 2004 to 2007 are studied. The National Lightning Detection Network is used to analyze flash density as a function of peak current and to evaluate the WWLLN. Flash density is shown to be smaller for hurricanes than for tropical depressions and storms, with this reduction being gradually more pronounced as flash peak current increases. The results suggest that flash density in the inner core is a parameter with potential for distinguishing intensifying versus nonintensifying TCs, particularly in the weaker storm stages where flash densities are largest. Vertical wind shear produces a strong downshear left (right) asymmetry in the inner core (outer rainbands), whereas motion asymmetries are less clear. The unprecedented azimuthal resolution used in this study suggests that as shear strengthens, the azimuthal region of convection in the inner core is sharpened from a width of ∼130° to a width of ∼60°. The radial distribution of flash density is shown to exhibit a relatively narrow region of little activity (between 60 and 120 km from the eye), with increased activity in both regions closer to, and more distant from, the center (i.e., the eyewall and outer rainbands, respectively). Finally, it is shown that the WWLLN captures the convective activity in Atlantic basin TCs remarkably well, despite its low detection efficiency.

Associations between Fermi Gamma‐ray Burst Monitor terrestrial gamma ray flashes and sferics from the World Wide Lightning Location Network

We report on a search for correlations between terrestrial gamma ray flashes (TGFs) detected by the Fermi Gamma‐ray Burst Monitor (GBM) and lightning strokes measured using the World Wide Lightning Location Network (WWLLN). We associate 15 of a total 50 GBM‐detected TGFs with individual discharges. We establish the relative timing between the TGF and the lightning stroke to an accuracy of &lt;50 μs, and find that in 13 of these 15 lightning‐TGF associations, the lightning stroke and the peak of the TGF are simultaneous to ∼40 μs. This suggests that a large fraction of TGFs are coincident with lightning discharges. The two nonsimultaneous associations do not show a consistent TGF‐lightning stroke temporal sequence. All 15 associations are with sferics within 300 km of the subspacecraft position. For those TGFs not correlated with a particular lightning stroke, we find storm activity within 300 km of the subspacecraft position in all but four of the TGFs. For three of these four TGFs, we find storm activity very close to one of the magnetic footprints of the spacecraft position. We associate the subspacecraft TGFs with gamma ray events and the footprint events with electrons traveling along magnetic field lines before hitting the Fermi spacecraft.

Observations of ozone production in a dissipating tropical convective cell during TC4

Abstract. From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times (15:12–17:00 UTC), providing a unique examination of ozone (O3) photochemistry on the edge of a convective cell. Ozone increased at a rate of ~1.6–4.6 ppbv/hr between the first and last ascent, resulting cell wide in an increase of ~(2.1–2.5) × 106 moles of O3. This estimate agrees to within a factor of two of our estimates of photochemical lightning O3 production from the WWLLN flashes, from the radar-inferred lightning flash data, and from the OMI NO2 data (~1.2, ~1.0, and ~1.7 × 106 moles, respectively), though all estimates have large uncertainties. Examination of DC-8 in situ and lidar O3 data gathered around the Gulf that day suggests 70–97% of the O3 change occurred in 2.5–5.1 km layer. A photochemical box model initialized with nearby TC4 aircraft trace gas data suggests these O3 production rates are possible with our present understanding of photochemistry.

Direct satellite observation of lightning-produced NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt;

Abstract. Lightning is an important source of NOx in the free troposphere, especially in the tropics, with strong impact on ozone production. However, estimates of lightning NOx (LNOx) production efficiency (LNOx per flash) are still quite uncertain. In this study we present a systematic analysis of NO2 column densities from SCIAMACHY measurements over active thunderstorms, as detected by the World-Wide Lightning Location Network (WWLLN), where the WWLLN detection efficiency was estimated using the flash climatology of the satellite lightning sensors LIS/OTD. Only events with high lightning activity are considered, where corrected WWLLN flash rate densities inside the satellite pixel within the last hour are above 1 /km2/h. For typical SCIAMACHY ground pixels of 30 × 60 km2, this threshold corresponds to 1800 flashes over the last hour, which, for literature estimates of lightning NOx production, should result in clearly enhanced NO2 column densities. From 2004–2008, we find 287 coincidences of SCIAMACHY measurements and high WWLLN flash rate densities. For some of these events, a clear enhancement of column densities of NO2 could be observed, indeed. But overall, the measured column densities are below the expected values by more than one order of magnitude, and in most of the cases, no enhanced NO2 could be found at all. Our results are in contradiction to the currently accepted range of LNOx production per flash of 15 (2–40)×1025 molec/flash. This probably partly results from the specific conditions for the events under investigation, i.e. events of high lightning activity in the morning (local time) and mostly (for 162 out of 287 events) over ocean. Within the detected coincidences, the highest NO2 column densities were observed around the US Eastcoast. This might be partly due to interference with ground sources of NOx being uplifted by the convective systems. However, it could also indicate that flashes in this region are particularly productive. We conclude that current estimates of LNOx production might be biased high for two reasons. First, we observe a high variability of NO2 for coincident lightning events. This high variability can easily cause a publication bias, since studies reporting on high NOx production have likely been published, while studies finding no or low amounts of NOx might have been rejected as errorneous or not significant. Second, many estimates of LNOx production in literature have been performed over the US, which is probably not representative for global lightning.

Cloud-to-ground lightning over Mexico and adjacent oceanic regions: a preliminary climatology using the WWLLN dataset

Abstract. This work constitutes the first climatological study of lightning over Mexico and adjacent oceanic areas for the period 2005–2009. Spatial and temporal distributions of cloud to ground lightning are presented and the processes that contribute to the lightning variability are analysed. The data are retrieved from the World Wide Lightning Location Network (WWLLN) dataset. The current WWLL network includes 40 stations which cover much of the globe and detect very low frequency radiation ("spherics") associated with lightning. The spatial distribution of the average yearly lightning over the continental region of Mexico shows the influence of orographic forcing in producing convective clouds with high lightning activity. However, a very high number of strikes is also observed in the States of Tabasco and Campeche, which are low-lying areas. This maximum is related to the climatological maximum of precipitation for the country and it may be associated with a region of persistent low-level convergence and convection in the southern portion of the Gulf of Mexico. The maps of correlation between rainfall and lightning provide insight into the microphysical processes occurring within the clouds. The maritime clouds close to the coastline exhibit similar properties to continental clouds as they produce very high lightning activity. The seasonal cycle of lightning registered by WWLLN is consistent with the LIS/OTD dataset for the selected regions. In terms of the annual distribution of cloud-to-ground strikes, July, August and September exhibit the highest number of strikes over continental Mexico. The diurnal cycle indicates that the maximum number of strikes over the continent is observed between 6 and 9 p.m. LT. The surrounding oceanic regions were subdivided into four distinct sectors: Gulf of Mexico, Caribbean, Sub-tropical Pacific and Tropical Pacific. The Gulf of Mexico has the broadest seasonal distribution, since during winter lightning associated with mid-latitude systems also affects the region. The diurnal distribution of lightning for the Gulf of Mexico exhibits the highest number of strokes at 9 a.m. The Caribbean seasonal distribution is slightly biased towards early fall, with a clear maximum observed during October. The diurnal distribution of lightning over the Caribbean is quite uniform with a slight increase near midnight. The Subtropical Pacific has the narrowest seasonal distribution, associated with the convection observed during the "North American Monsoon", with the maximum number of strikes during August and September. In contrast, the Tropical Pacific has a broader seasonal cycle, associated with convection in the Inter-Tropical Convergence Zone (ITCZ), starting in May and lasting till October. In both adjacent Pacific regions, the strikes present a maximum in the early morning, the time of the highest frequency of land breeze.

VLF electromagnetic background in the seismoactive area of Northern Vietnam

The preliminary results of observations of VLF electromagnetic signals (atmospherics) in the mountains of North Vietnam (Dien Bien Phu, 21°23′50″ N, 103°0′28″ E) are presented. Primarily, signals of typical atmospherics with a maximum in the frequency range of 4–9 kHz were observed; sometimes they were accompanied by so-called “tails” at frequencies less than 1 kHz, and also tweeks of usually short duration (about 10 ms) were observed. Several parameters of the ionosphere, as well as the distance to sources of atmospherics (in accordance to the data of the World Wide Lightning Location Network (TOGA)), were estimated by spectral-temporal characteristics of tweeks.

An evaluation of the Worldwide Lightning Location Network (WWLLN) using the National Lightning Detection Network (NLDN) as ground truth

A performance assessment of the Worldwide Lightning Location Network (WWLLN) is presented using the National Lightning Detection Network (NLDN) as ground truth, over unprecedented time and spatial scales. The study spans 3 years, from 5 April 2006 to 31 March 2009, throughout the contiguous United States. The capabilities of the network are shown to improve greatly from the first to the third year of the study, with an overall detection efficiency of cloud‐to‐ground flashes increasing from 3.88% in 2006−2007 to 10.30% in 2008−2009. The WWLLN cloud‐to‐ground detection efficiency is found to be strongly dependent on peak current and polarity, attaining values larger than 10% (35%) for currents stronger than ±35 kA (−130 kA) and values less than 2% for currents between 0 and −10 kA. The location accuracy is found to have a northward and westward bias, with average location errors of 4.03 km in the north‐south and 4.98 km in the east‐west directions, respectively. The WWLLN is shown to have strong limitations in capturing the diurnal cycle, missing both the timing of the maximum and minimum lightning activity (around 1600 and 0900 LT, respectively), and the amplitude of the cycle as well. It is found that in 3 h intervals, the number of flashes in the WWLLN has some proportionality to the number of flashes in the NLDN, suggesting that the WWLLN has strong potential for meteorological applications.

A performance assessment of the World Wide Lightning Location Network (WWLLN) via comparison with the Canadian Lightning Detection Network (CLDN)

Abstract. The World Wide Lightning Location Network (WWLLN) uses globally-distributed Very Low Frequency (VLF) receivers in order to observe lightning around the globe. Its objective is to locate as many global lightning strokes as possible, with high temporal and spatial (&lt; 10 km) accuracy. Since detection is done in the VLF range, signals from high peak current lightning strokes are able to propagate up to ~104 km before being detected by the WWLLN sensors, allowing for receiving stations to be sparsely spaced. Through a comparison with measurements made by the Canadian Lightning Detection Network (CLDN) between May and August 2008 over a 4° latitude by 4° longitude region centered on Toronto, Canada, this study found that WWLLN detection was most sensitive to high peak current lightning strokes. Events were considered shared between the two networks if they fell within 0.5 ms of each other. Using this criterion, 19 128 WWLLN strokes (analyzed using the Stroke_B algorithm) were shared with CLDN lightning strokes, producing a detection efficiency of 2.8%. The peak current threshold for WWLLN detection is found to be ~20 kA, with its detection efficiency increasing from 11.3% for peak currents greater than 20 kA to 75.8% for peak currents greater than 120 kA. The detection efficiency is seen to have a clear diurnal dependence, with a higher detection efficiency at local midnight than at local noon; this is attributed to the difference in the thickness of the ionospheric D-region between night and day. The mean time difference (WWLLN − CLDN) between shared events was −6.44 μs with a standard deviation of 35 μs, and the mean absolute location accuracy was 7.24 km with a standard deviation of 6.34 km. These results are generally consistent with previous comparison studies of the WWLLN with other regional networks around the world. Additional receiver stations are continuously being added to the network, acting to improve this detection efficiency.

Terrestrial gamma ray flashes correlated to storm phase and tropopause height

We compare the seasonal and geographical occurrence of terrestrial gamma ray flashes (TGFs) with global lightning maps and find that only part of the difference can be explained by differences in tropopause altitude. The altitude hypothesis suggests either that TGFs are produced only in conjunction with the highest lightning or that only the highest events are seen from space because of the easier escape of gamma rays from the atmosphere. We find that the differences in atmospheric transmission due to seasonal and geographical differences in tropopause height play a major but not dominant role in reconciling lightning and TGF maps and that other factors are needed to explain the remaining local differences. In a second analysis, we use radio atmospherics data from the World Wide Lightning Location Network to study at what time in the evolution of a storm TGFs tend to be seen. We find that, on average, TGFs lag the peak flash rate of the associated storm by 38 min, although the range of lags is extremely wide, including some cases where the TGF leads the peak flash rate.