European Cooperation For Lightning Detection Research Articles

Thunderstorm environments in Europe

Abstract. Meteorological environments favorable for thunderstorms are studied across Europe, including rare thunderstorm conditions from seasons with climatologically few thunderstorms. Using cluster analysis on ERA5 reanalysis data and EUCLID (European Cooperation for Lightning Detection) lightning data, two major thunderstorm environments are found: wind-field thunderstorms, characterized by increased wind speeds, high shear, strong large-scale vertical velocities, and low CAPE values compared to other thunderstorms in the same region, and mass-field thunderstorms, characterized by large CAPE values, high dew point temperatures, and elevated isotherm heights. Wind-field thunderstorms occur mainly in winter and more over the seas, while mass-field thunderstorms occur more frequently in summer and over the European mainland. Several sub-environments of these two major thunderstorm environments exist. Principal component analysis is used to identify four topographically distinct regions in Europe that share similar thunderstorm characteristics: the Mediterranean, Alpine–central, continental, and coastal regions, respectively. Based on these results it is possible to differentiate lightning conditions in different seasons from coarse reanalysis data without a static threshold or a seasonal criterion.

A Pan-Alpine Climatology of Lightning and Convective Initiation

Abstract A new lightning-flash and convective initiation climatology is developed over the Alpine area, one of the hotspots for lightning activity in Europe. The climatology uses cloud-to-ground (CG) data from the European Cooperation for Lightning Detection (EUCLID) network, occurring from 2005 to 2019. The CG lightning data are gridded at a resolution of approximately 2 km and 10 min. A new and simple method of identifying convective initiation (CI) events applies a spatiotemporal mask to the CG data to determine CI timing and location. Although the method depends on a few empirical thresholds, sensitivity tests show the results to be robust. The maximum activity for both CG flashes and CI events is observed from mid-May to mid-September, with a peak at the end of July; the peak in the diurnal cycle occurs in the afternoon. CI is mainly concentrated over and around the Alps, particularly in northern and northeastern Italy. Since many thunderstorms follow the prevailing midlatitude westerly flow, a peak of CG flashes extends from the mountains into the plains and coastal areas of northeastern Italy and Slovenia. CG flashes and CI events over the sea/coast occur less frequently than in plains and mountains, have a weaker diurnal cycle, and have a seasonal maximum in autumn instead of summer.

Quantification of lightning-produced NO<sub><i>x</i></sub> over the Pyrenees and the Ebro Valley by using different TROPOMI-NO<sub>2</sub> and cloud research products

Abstract. Lightning, one of the major sources of nitrogen oxides (NOx) in the atmosphere, contributes to the tropospheric concentration of ozone and to the oxidizing capacity of the atmosphere. Lightning produces between 2 and 8 Tg N yr−1 globally and on average about 250 ± 150 mol NOx per flash. In this work, we estimate the moles of NOx produced per flash (LNOx production efficiency) in the Pyrenees (Spain, France and Andorra) and in the Ebro Valley (Spain) by using nitrogen dioxide (NO2) and cloud properties from the TROPOspheric Monitoring Instrument (TROPOMI) as well as lightning data from the Earth Networks Global Lightning Network (ENGLN) and from the EUropean Co-operation for LIghtning Detection (EUCLID). The Pyrenees are one of the areas in Europe with the highest lightning frequencies, which, along with their remoteness as well as their very low NOx background, enables us to better distinguish the LNOx signal produced by recent lightning in TROPOMI NO2 measurements. We compare the LNOx production efficiency estimates for eight convective systems in 2018 using two different sets of TROPOMI research products provided by the Royal Netherlands Meteorological Institute (KNMI) and the Deutsches Zentrum für Luft- und Raumfahrt (DLR). According to our results, the mean LNOx production efficiency in the Pyrenees and in the Ebro Valley, using a 3 h chemical lifetime, ranges between 14 and 103 mol NOx per flash from the eight systems. The mean LNOx production efficiency estimates obtained using both TROPOMI products and ENGLN lightning data differ by ∼ 23 %, while they differ by ∼ 35 % when using EUCLID lightning data. The main sources of uncertainty when using ENGLN lightning data are the estimation of background NOx that is not produced by lightning and the time window before the TROPOMI overpass that is used to count the total number of lightning flashes contributing to freshly produced LNOx. The main source of uncertainty when using EUCLID lightning data is the uncertainty in the detection efficiency of EUCLID.

A 10-year study on the lightning activity in Italy using data from the SIRF network

Lightning is one of the most dangerous natural phenomena, able to produce high impacts and damage on human beings and infrastructures (civil, electric, telecommunications, etc..) even though perception of it as a hazard is low. The aim of this study is to provide a detailed analysis of lightning occurrence throughout the Italian territory to support the work of different operators and researchers (physicists, meteorologists and electric/ITC engineers) improving knowledge about the main properties of lightning. Thus, an in-depth study of the statistics of lightning activity across the Italian territory for the period 2010–2019 is performed in detail using the data collected by the Italian Lightning Detection Network SIRF (Sistema Italiano Rilevamento Fulmini), part of the European network EUCLID (European Cooperation for Lightning Detection). This analysis presents general properties such as Ground Stroke Density (GSD) and the positive to negative strokes ratio by highlighting how seasonal, geographical and orographic factors influence their values. Then, attention is focused on lightning peak current, on flash multiplicity and on the distance between the points of impact of different strokes within a flash. Comparison made with other articles available in the literature reveals good agreement with studies conducted with other LLS data in Mediterranean regions. On the other hand, some differences appear with direct current measurements that can be partly ascribed to Lightning Location System (LLS) detection contamination (confirming other comparative studies of LLS and instrumented tower findings), to differences between tower and ground measures, and to the presence of regional differences.

Comparing lightning observations of the ground-based European lightning location system EUCLID and the space-based Lightning Imaging Sensor (LIS) on the International Space Station (ISS)

Abstract. The Lightning Imaging Sensor (LIS) on the International Space Station (ISS), hereafter referred to as ISS-LIS, detects lightning from space by capturing the optical scattered light emitted from the top of the clouds. The ground-based European Cooperation for Lightning Detection (EUCLID) makes use of the low-frequency electromagnetic signals generated by lightning discharges to locate them accordingly. The objective of this work is to quantify the similarities and contrasts between these two distinct lightning detection technologies by comparing the EUCLID cloud-to-ground strokes and intracloud pulses to the ISS-LIS groups in addition to the correlation at the flash level. The analysis is based on the observations made between 1 March 2017 and 31 March 2019 within the EUCLID network and limited to 54∘ north. A Bayesian approach is adopted to determine the relative and absolute detection efficiencies (DEs) of each system. It is found that the EUCLID relative and absolute flash DE improves by approximately 10 % towards the center of the EUCLID network up to a value of 56.3 % and 69.0 %, respectively, compared to the averaged value over the full domain, inherent to the network geometry and sensor technology. In contrast, the relative and absolute ISS-LIS flash DE over the full domain is 48.4 % and 71.3 %, respectively, and is somewhat higher than the values obtained in the center of the EUCLID network. The behavior of the relative DE of each system in terms of the flash characteristics of the other reveals that the greater the value, the more likely the other system will detect the flash. For instance, when the ISS-LIS flash duration is smaller than or equal to 200 ms, the EUCLID relative flash DE drops below 50 %, whereas it increases up to 80 % for ISS-LIS flashes with a duration longer than 750 ms. Finally, the distribution of the diurnal DE indicates a higher DE for the ISS-LIS and a lower DE for EUCLID at night.

High-Resolution Lightning Detection and Possible Relationship with Rainfall Events over the Central Mediterranean Area

Lightning activity is usually associated with precipitations events and represents a possible indicator of climate change, even contributing to its increase with the production of NOx gases. The study of lightning activity on long temporal periods is crucial for fields related to atmospheric phenomena from intense rain-related hazard processes to long-term climate changes. This study focuses on 19 years of lightning-activity data, recorded from Italian Lightning Detection Network SIRF, part of the European network EUCLID (European Cooperation for Lightning Detection). Preliminary analysis was dedicated to the spatial and temporal assessment of lightning through detection in the Central Mediterranean area, focusing on yearly and monthly data. Temporal and spatial features have been analyzed, measuring clustering through the application of global Moran’s I statistics and spatial local autocorrelation; a Mann–Kendall trend test was performed on monthly series aggregating the original data on a 5 × 5 km cell. A local statistically significant trend emerged from the analysis, suggesting possible linkage between surface warming and lightning activity.

A Climatology of Thunderstorms across Europe from a Synthesis of Multiple Data Sources

AbstractThe climatology of (severe) thunderstorm days is investigated on a pan-European scale for the period of 1979–2017. For this purpose, sounding measurements, surface observations, lightning data from ZEUS (a European-wide lightning detection system) and European Cooperation for Lightning Detection (EUCLID), ERA-Interim, and severe weather reports are compared and their respective strengths and weaknesses are discussed. The research focuses on the annual cycles in thunderstorm activity and their spatial variability. According to all datasets thunderstorms are the most frequent in the central Mediterranean, the Alps, the Balkan Peninsula, and the Carpathians. Proxies for severe thunderstorm environments show similar patterns, but severe weather reports instead have their highest frequency over central Europe. Annual peak thunderstorm activity is in July and August over northern, eastern, and central Europe, contrasting with peaks in May and June over western and southeastern Europe. The Mediterranean, driven by the warm waters, has predominant activity in the fall (western part) and winter (eastern part) while the nearby Iberian Peninsula and eastern Turkey have peaks in April and May. Trend analysis of the mean annual number of days with thunderstorms since 1979 indicates an increase over the Alps and central, southeastern, and eastern Europe with a decrease over the southwest. Multiannual changes refer also to changes in the pattern of the annual cycle. Comparison of different data sources revealed that although lightning data provide the most objective sampling of thunderstorm activity, short operating periods and areas devoid of sensors limit their utility. In contrast, reanalysis complements these disadvantages to provide a longer climatology, but is prone to errors related to modeling thunderstorm occurrence and the numerical simulation itself.

Analysis of lightning outliers in the EUCLID network

Abstract. Lightning data as observed by the European Cooperation for Lightning Detection (EUCLID) network are used in combination with radar data to retrieve the temporal and spatial behavior of lightning outliers, i.e., discharges located in a wrong place, over a 5-year period from 2011 to 2016. Cloud-to-ground (CG) stroke and intracloud (IC) pulse data are superimposed on corresponding 5 min radar precipitation fields in two topographically different areas, Belgium and Austria, in order to extract lightning outliers based on the distance between each lightning event and the nearest precipitation. It is shown that the percentage of outliers is sensitive to changes in the network and to the location algorithm itself. The total percentage of outliers for both regions varies over the years between 0.8 and 1.7 % for a distance to the nearest precipitation of 2 km, with an average of approximately 1.2 % in Belgium and Austria. Outside the European summer thunderstorm season, the percentage of outliers tends to increase somewhat. The majority of all the outliers are low peak current events with absolute values falling between 0 and 10 kA. More specifically, positive cloud-to-ground strokes are more likely to be classified as outliers compared to all other types of discharges. Furthermore, it turns out that the number of sensors participating in locating a lightning discharge is different for outliers versus correctly located events, with outliers having the lowest amount of sensors participating. In addition, it is shown that in most cases the semi-major axis (SMA) assigned to a lightning discharge as a confidence indicator in the location accuracy (LA) is smaller for correctly located events compared to the semi-major axis of outliers.

The European lightning location system EUCLID – Part 2: Observations

Abstract. Cloud-to-ground (CG) lightning data from the European Cooperation for Lightning Detection (EUCLID) network over the period 2006–2014 are explored. Mean CG flash densities vary over the European continent, with the highest density of about 6 km−2 yr−1 found at the intersection of the borders between Austria, Italy and Slovenia. The majority of lightning activity takes place between May and September, accounting for 85 % of the total observed CG activity. Furthermore, the thunderstorm season reaches its highest activity in July, while the diurnal cycle peaks around 15:00 UTC. A difference between CG flashes over land and sea becomes apparent when looking at the peak current estimates. It is found that flashes with higher peak currents occur in greater proportion over sea than over land.

Evaluation of the performance characteristics of the European Lightning Detection Network EUCLID in the Alps region for upward negative flashes using direct measurements at the instrumented Säntis Tower

AbstractIn this paper, we present a performance analysis of the European Cooperation for Lightning Detection (EUCLID) lightning detection network using data obtained on lightning currents measured at the Säntis Tower (located in northeastern of Switzerland) from June 2010 to December 2013. In the considered period of analysis, a total number of 269 upward negative flashes were recorded at the Säntis Tower. The performance of the EUCLID lightning detection network is evaluated in terms of detection efficiency, location accuracy, and peak current estimates for upward flashes. Excluding flashes containing only an initial continuous current with no superimposed pulses exceeding 2 kA, the flash detection efficiency for upward flashes is estimated to be 97%. The recorded flashes contained a total of 2795 pulses (including return strokes and International Conference on Communications pulses characterized by risetimes lower than 8 µs and peaks greater than 2 kA). The overall pulse detection efficiency was found to be 73%. For pulses with peak values higher than 5 kA, the pulse detection efficiency was found to be about 83%. Peak current estimates provided by the EUCLID network were found to be significantly larger than their directly measured counterparts. This overestimation might be attributed to the enhancement of the radiated electromagnetic fields associated with the presence of the tower and the mountain. The median of the absolute distance error, defined as the median distance between the Säntis Tower location and the EUCLID's stroke locations, was found to be 186 m, the majority of large location errors being associated with measured current peaks lower than 10 kA. The analysis revealed also that the location accuracy of the EUCLID network improved significantly in 2013 as a result of an upgrade in the location algorithms to take into account propagation effects.

A 10-Year Study on the Characteristics of Thunderstorms in Belgium Based on Cloud-to-Ground Lightning Data

Abstract Temporal and spatial distributions of cloud-to-ground (CG) lightning in Belgium are analyzed. Based on data from the European Cooperation for Lightning Detection (EUCLID) network, spanning a period of 10 years between 2004 and 2013, mean CG flash densities vary between 0.3 km−2 yr−1 in the west up to 2.4 km−2 yr−1 toward the east of Belgium, with an average flash density of 0.7 km−2 yr−1. The same behavior is found in terms of thunderstorm days and hours, where in the east most of the activity is observed, with a drop-off toward the coast. The majority of lightning activity takes place in the summer months between May and August, accounting for nearly 90% of the total activity. Furthermore, the thunderstorm season reaches its highest activity in July in terms of CG detections, while the diurnal cycle peaks between 1500 and 1600 UTC. A correlation is found between the estimated peak currents and altitude, with on average higher absolute peak currents at lower elevations and vice versa. In addition, a cell tracking algorithm is applied to the data to monitor the behavior of the individual cells. It is found that the lightning cells travel at an average speed of about 25 km h−1, with a preferred northeasterly direction of movement. At last, CG flash rates are strongly related to the cell area.

A cloud-to-ground lightning climatology for north-eastern Italy

Abstract. This study analyzes the spatial distribution and temporal characteristics of cloud-to-ground lightnings (C2G) in the North East of Italy and the neighboring areas of Austria, Slovenia and Croatia. The dataset consists of about 6.5 millions C2G flash records, both positive and negative, observed between January 1995 and December 2011 by the "Centro Elettrotecnico Sperimentale Italiano-Sistema Italiano Rilevamento Fulmini'' (CESI/SIRF), part of the European Cooperation for Lightning Detection (EUCLID) Network. The results show that C2G lightnings concentrate in the foothill regions on the southern flank of the Eastern Alps with a maximum of discharge frequency of 10 lightnings per km2 per year. The number of C2G strokes varies with the period of the year: the most active period for lightning starts in April and lasts through November with the highest number of C2G strokes happening during the summer months of July and August, with maximum spatial density slightly moving from the mountain to the coastal area. The least frequency of C2G strokes is observed during wintertime. The mean diurnal C2G lightning activity for the whole domain shows a peak around 16:00–17:00 UTC and reaches a minimum around 07:00–09:00 UTC; the mean spatial distribution follows different patterns depending on the period of the day.

Performance Characteristics of Distinct Lightning Detection Networks Covering Belgium

Abstract This study reports results from electric field measurements coupled to high-speed camera observations of cloud-to-ground lightning to test the performance of lightning location networks in terms of its detection efficiency and location accuracy. The measurements were carried out in August 2011 in Belgium, during which 57 negative cloud-to-ground flashes, with a total of 210 strokes, were recorded. One of these flashes was followed by a continuing current of over 1 s—one of the longest ever observed in natural negative cloud-to-ground lightning. Lightning data gathered from the lightning detection network operated by the Royal Meteorological Institute of Belgium [consisting of a network employing solely Surveillance et Alerte Foudre par Interférométrie Radioélectrique (SAFIR) sensors and a network combining SAFIR and LS sensors], the European Cooperation for Lightning Detection (EUCLID), Vaisala’s Global Lightning Detection network GLD360, and the Met Office’s long-range Arrival Time Difference network (ATDnet) are evaluated against this ground-truth dataset. It is found that all networks are capable of detecting over 90% of the observed flashes, but a larger spread is observed at the level of the individual strokes. The median location accuracy varies between 0.6 and 1 km, except for the SAFIR network, locating the ground contacts with 6.1-km median accuracy. The same holds for the reported peak currents, where a good correlation is found among the networks that provide peak current estimates, apart from the SAFIR network being off by a factor of 3.

Lightning Density Distribution and Hazard in an Alpine Region

Due to the expected climate change driven increase of extreme weather events, damage risks for infrastructure and buildings are rising. Hence spatial decision-support material is necessary to enhance risk management and planning strategies. The presented study contributes to this topic by means of an analysis of cloud-to-ground lightning patterns and their impact on structural facilities using Geographic Information Systems (GIS). Lightning records from 1998 to 2009, ascertained by the European Cooperation for Lightning Detection (EUCLID), were utilized in order to apply three different lightning density approaches to an alpine area comprising the Austrian federal province of Salzburg and south- east Bavaria, Germany. Based on the derived lightning density distribution maps and an elevation model, spatial coherences between lightning activity and various topographic properties such as altitude or surface curvature were evaluated. In order to subsequently estimate the lightning hazard to buildings in the city of Salzburg, the frequencies of hazardous lightning events were estimated in GIS using a European lightning protection standard (EN62305-2 Risk Management) as a foundation. Thereby, the prototypical realization was based on the lightning density, a cadastral dataset, and elevation data. The lighting density results obtained show high lightning activity with more than 3 yearly flashes per square kilometer along the northern edge of the Alps. The hazard analysis in the city of Salzburg showed high hazards for buildings due to electromagnetic induction (up to one dangerous event in each year) and comparatively low hazards due to direct lightning strikes (one dangerous event every 10 to 2200 years).

The comparison of GLD360 and EUCLID lightning location systems in Europe

AbstractThe performance of GLD360 (Global Lightning Dataset 360) long range lightning location system has been studied over Europe. The analysis has been done by comparing the lightning location data of GLD360 from year 2011 (May–September) to a reference system, which here is EUCLID (European Cooperation for Lightning Detection); EUCLID is a good reference system because its performance has been analyzed around Europe in many previous studies, especially in Austria. We show results about the relative performance of GLD360 from Austria, Scandinavia, North Sea and Spain, as well as the general relative performance over the whole Europe. Our results indicate that (i) the relative detection efficiency (RDE) of GLD360 varies from about 36% to 170% in the EUCLID coverage area, (ii) GLD360 daily RDE in Austria in July varies from 4.4% to 80.8%, (iii) the median relative location accuracy of GLD360 in Austria in July is 2.8km, (iv) the diurnal variation in Austria in July shows similar feature for both systems, i.e., largest percentage at 16–17 UTC, (v) the median peak current of negative (positive) strokes for GLD360 is 14kA (11kA) and for EUCLID for the same area and period 9kA (7kA), (vi) the correlation between EUCLID and GLD360 peak current is r=0.72, and (vii) the boundary of the efficient detection area of EUCLID can be clearly seen when the GLD360 RDE increases above 100%; this coverage boundary is extremely sharp. Our results show that a comparison of this kind reveals many interesting performance issues regarding both the comparative and the reference network, especially the areas where the reference network performs poorly.

Benford's Law and Its Application to Lightning Data

Benford's law applies to a wide variety of natural and man-made datasets and it has been successfully applied to test the integrity of data and to detect possible fraud and anomalous results in economy, politics, and management studies. In this paper, we investigate the applicability of Benford's law to lightning data. To do this, we use lightning data in Switzerland obtained using the European Cooperation for Lightning Detection (EUCLID) network. The considered dataset consists of the cloud-to-ground flashes in Switzerland for the period from 1999 till 2007. First the total number of negative and positive flashes per day is considered in the analysis. It is shown that the obtained distribution is in very good agreement with Benford's law. The same analysis is repeated considering in the dataset only the flashes containing return strokes with absolute peak currents lower than 5 kA, for which the detection efficiency of the lightning location network is expected to be lower. The resulting distribution shows less agreement with Benford's law. The obtained results suggest that Benford's law may find an interesting application in the evaluation of the detection efficiency of a given lightning location network.

Evaluation of thunderstorm indices from ECMWF analyses, lightning data and severe storm reports

This study describes the environmental atmospheric characteristics in the vicinity of different types of severe convective storms in Europe during the warm seasons in 2006 and 2007. 3406 severe weather events from the European Severe Weather Database ESWD were investigated to get information about different types of severe local storms, such as significant or weak tornadoes, large hail, damaging winds, and heavy precipitation. These data were combined with EUCLID (European Cooperation for Lightning Detection) lightning data to distinguish and classify thunderstorm activity on a European scale into seven categories: none, weak and 5 types of severe thunderstorms. Sounding parameters in close proximity to reported events were derived from daily high-resolution T799 ECMWF (European Centre for Medium-range Weather Forecasts) analyses. We found from the sounding-derived parameters in Europe: 1) Instability indices and CAPE have considerable skill to predict the occurrence of thunderstorms and the probability of severe events. 2) Low level moisture can be used as a predictor to distinguish between significant tornadoes or non-severe convection. 3) Most of the events associated with wind gusts during strong synoptic flow situations reveal the downward transport of momentum as a very important factor. 4) While deep-layer shear discriminates well between severe and non-severe events, the storm-relative helicity in the 0–1 km and especially in the 0–3 km layer adjacent to the ground has more skill in distinguishing between environments favouring significant tornadoes and wind gusts versus other severe events. Additionally, composite parameters that combine measurements of buoyancy, vertical shear and low level moisture have been tested to discriminate between severe events.