Cluster Analysis Algorithms for RS and WWLLN Data Processing

This study evaluates 4 years (2009–2012) of World Wide Lightning Location Network (WWLLN) data relative to the Tropical Rainfall Measuring Mission Lightning Imaging Sensor (LIS). In the Western Hemisphere, between 38°N and 38°S, the WWLLN detection efficiency (DE) (of LIS flashes) steadily improves from 6% during 2009 to 9.2% during 2012. The WWLLN is approximately three times more likely to detect a LIS flash over the ocean (17.3%) than over land (6.4%), and DE values greater than 20% only occur over the oceans. An average of 1.5 WWLLN strokes occurs during each matched LIS flash, but 71.5% of matched flashes are single stroke. Matched LIS flashes have more events/groups, longer durations, and larger areas than non‐matched flashes. The close spatial proximity (11 km) and temporal proximity (+62 ms) between matched WWLLN and LIS flashes are important for Geostationary Lighting Mapper risk reduction studies that use existing networks to develop proxy data sets.

This paper aims to study the influence of thunderstorm intensity on forest fire occurrence in the Altai Republic, a region with valuable forest resources and high fire hazard. Given that thunderstorms are one of the main sources of ignition, understanding this relationship is critical for developing effective forest fire prevention and control strategies. The aim of the study is to identify forest management areas in the Altai Republic where the most pronounced correlation between the number of registered forest fires and the frequency of lightning strikes is observed. This will optimize the allocation of resources for instrumental observations of thunderstorm activity, focusing on those areas where the risk of forest fires is highest. To solve this problem, the authors used forest fire data provided by the Ministry of Emergency Situations in the Altai Republic for the period from 2020 to 2024, which provides an up-to-date picture of the fire situation in the region. Additionally, the work used data from the World Wide Lightning Location Network, which contains information about the exact time and coordinates of lightning discharges for the same time period.

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.

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.

Synoptic and mesoscale cyclonic systems over the ocean and seas are often accompanied by thunderstorm activity, the intensity and spatial distribution of which is modulated by the dynamic structure of these systems. Lightning discharges are sources of electromagnetic radiation in the range of very low frequencies (VLF) and are detected by VLF location finders. Using the World Wide Lightning Location Network (WWLLN), relations between characteristics of fields of detected lightning discharges in the north-western part of the Pacific Ocean and those of fields of meteorological elements of weather formations estimated by data of remote sensing of the Earth by satellites are studied by an example of tropical cyclones. We illustrate a technique permitting one to connect thunderstorm activity parameters (frequency and intensity, as well as spatial distribution of lightning discharges) with the structure of weather systems over oceans and seas and with the intensity and forms of mesoscale formations distinguished in these systems by fields of the near-water wind vortex (the fields are obtained using a scatterometer) and by satellite images in the visible and infrared ranges. The relations between the frequency and density of lightning discharges in the range of influence of a tropical cyclone (TC) and spatial distribution of the near-water wind vortex are demonstrated by an example of individual TCs of 2005–2013.

The paper investigates lightning activity in the region of tropical cyclones (TC), its structure and changeability during the process of TC development and attenuation according to the data of the World Wide Lightning Location Network (WWLLN) as well as the relation with ocean surface wind fields according to the ASCAT scatterometer data. Distribution of lightning discharges in TC regions and discharge density fields drawn up from them allowed us to detect TC structure elements, such as mesovortexes, eyewalls, cloud bands and spirals, and to trace their change in space and time.

Abstract. According to World Wide Lightning Location Network (WWLLN) data, a sequence of lightning discharges was detected which occurred in the area of the explosive eruption of Shiveluch volcano on 16 November 2014 in Kamchatka. Information on the ash cloud motion was confirmed by the measurements of atmospheric electricity, satellite observations and meteorological and seismic data. It was concluded that WWLLN resolution is enough to detect the earlier stage of volcanic explosive eruption when electrification processes develop the most intensively. The lightning method has the undeniable advantage for the fast remote sensing of volcanic electric activity anywhere in the world. There is a good opportunity for the development of WWLLN technology to observe explosive volcanic eruptions.

On Aug. 29, 2016, the tropical cyclone Lionrock was reported to turn into an extra-tropical storm and go to the shore of the Primorsky Region as monitoring shows, which brought about significant precipitation growth recorded in the north of the coast. Many surveys show the tropical cyclones in this area to transform into extra-tropical ones and become powerful mid-latitude storms with significant damage to coastal and maritime areas. The paper uses WWLLN (World Wide Lightning Location Network) data to study the thunderstorm activity while the tropical cyclone reaches the typhoon level with the maximum wind velocity. This made it possible to identify parameters’ variations of thunderstorm activity during atmospheric vortex phenomena. It also enabled us to determine the emergency probability due to a thunderstorm.

The present article describes a new concept of lightning-caused forest fire danger using a probabilistic criterion. The assessment of forest fire danger is made on the basis of the algorithm that classifies the forest territory by vegetation conditions. Lightning activity is processed by the MODIS spectroradiometer according to the World Wide Lightning Location Network data and remote sensing data for the Timiryazevskiy forestry in the Tomsk Region. The cluster analysis of the WWLLN and MOD06_L2 product data are used in the present paper.

The averaged data of observations oflightning strikes in North Asia in 2009-2014 are presented. The pattern is retrieved from the data of World Wide Lightning Location Network (WWLLN); one station of this network is located in Yakutsk. The dependence of thunderstorm activity on latitude, longitude, and altitude is demonstrated.

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.

Context. The components of the geoinformation system for monitoring, forecasting and assessment of forest fire danger caused by thunderstorm activity are developed. Objective of the work is to create an embedded software tool for physically based forecasting, monitoring and evaluation of the probability of forest fire occurrence as a result of the impact of a lightning discharge on a tree trunk. Method. Structural analysis is used to design elements and information flows inside and outside of the developed geographic information system. Mathematical modeling is used to determine the parameters of tree ignition by the cloud-to-ground lightning discharge. Mathematically, the process of tree trunk heating is described using a system of non-stationary heat conduction equations with a source part responsible for the heat release according to the Joule-Lenz law in the core of the tree trunk. The finite difference method is used to solve the differential heat equation. Finite-difference analogues are solved by the double-sweep method. Program realization is implemented in the built-in high-level language. The probability theory (conditional probability) is used to develop a probabilistic criterion for forest fire danger estimation. Results. A software tool is developed to estimate the tree ignition delay time as a result of the impact of a cloud-to-ground lightning discharge. The GIS-system component is developed in the high-level programming language Python. We have obtained probability distribution of forest fire occurrences from thunderstorms for the territory of the Timiryazevsky forestry in the Tomsk region is obtained. Conclusions. We have proposed a physically proved method for forecasting, monitoring and assessing forest fire danger caused by thunderstorm activity. The deterministic mathematical model is used to simulate tree ignition by the cloud-to-ground lightning discharge in conjunction with the probabilistic criterion for assessing forest fire danger. We have analysed forest fire danger for a typical territory of the Tomsk region (Timiryazevskiy forestry).

The Ozone Monitoring Instrument (OMI) on board the NASA Aura satellite was launched into sun-synchronous low-earth orbit in 2004. Its hyperspectral measurements have been an invaluable tool in determining trace-gas concentrations in the troposphere and stratosphere. Nitrogen dioxide (NO2) has a particularly prominent absorption signature in the violet and near-UV regions of the OMI spectrum. This signature can be exploited in retrievals of column amounts of NO2 attributable to both natural and anthropogenic sources. We outline the OMI NO2 retrieval algorithm and demonstrate its utility for inferring NOx (NO + NO2) amounts due to lightning. Lightning is the dominant source of NOx in the free troposphere, and most estimates of the concentration of lightning NOx (LNOx) require knowledge of the amount of this species produced per lightning flash. We present the largest spatial- and temporal-scale investigation of LNOx to date that combines satellite-based NOx estimates and lightning flash data. The study comprises five northern-hemisphere (NH) summers, including much of the mid-latitude regions in North America and Asia and adjacent waters. NO2 measurements are converted to LNOx and compared with flashes preceding OMI overpass by 2 hours. The flash counts are derived from ground-based World Wide Lightning Location Network (WWLLN) data that are adjusted for detection efficiency. We find reasonable correlation between the number of lightning flashes and the amount of LNOx produced and estimate mean efficiencies for the production of LNOx in various NH regions. Overall results indicate mole/flash values near the low end of those reported in previous LNOx studies, as well as a possible dependence of production efficiency on flash rate. These findings have potential implications in the chemistry of upper tropospheric trace gases and the global NOx budget.

Characterization of the lightning activity of “Relámpago del Catatumbo”

A parallel VLF radio noise spectrometer has been used at a testing ground of the ShICRA SB RAS for recording ionospheric-magnetospheric radio emissions since 1972. The site located at a distance of 30 km from Yakutsk (62 N, 129.72 E). A one-point lightning discharge recorder was also installed at the site, which consists of a whip and two crossed loop antennas, an amplifier, an ADC, and a PC with a special program. The same direction finder with a change in gain and a special program can work as a narrow-sector direction finder for fluctuating radio noise. To investigate the function of propagation of VLF signals, narrowband radio noise, and their dependence on the space weather parameters, a VLF signal recorder that has been operating continuously in Yakutsk since 2009 is used. The World Wide Lightning Location Network (wwlln.net) data have been used for lightning discharge location since 2009. One of the WWLLN receivers was installed in Yakutsk. One-point lightning guides called “LD-250” and “Storm Tracker” for recording the coordinates of a lightning discharge and its type have been used for discharge registration within a territory of 400 km in radius around Yakutsk since 2006.