Needle Propagation and Twinkling Characteristics

Recently, a new lightning phenomena, termed needles, has been observed in both VHF and in optical along positive lightning leaders. They appear as small (<100 m) leader branches that undergo dielectric breakdown at regular intervals (called twinkles). Providing a coherent and consistent explanation for this phenomenon is challenging as each twinkle is a form of negative breakdown that propagates away from the positive leader. In this study, we provide detailed observations of needles in VHF, observed during two lightning flashes. We show distributions of different needle properties, including twinkle propagation speeds, time between twinkles, and needle lengths, among others. We show a return stroke and multiple recoil leaders that quench needle activity. We also show that nearby needle activity does not seem to correlate together, and that needle twinkling can slow down by 10%–30% per twinkle. We conclude by presenting possibilities for how the positive leader could induce negative propagation away from the positive channel, and we argue that twinkles can propagate like a stepped leader or like a recoil leader depending on the temperature of the needle, which implies that needle twinkles can probably propagate without emitting VHF

Morphologie de sprites et conditions de productions de sprites et de jets dans les systèmes orageux de méso-échelle

Ce document décrit l'analyse des conditions de production de phénomènes lumineux transitoires dans la mésosphère, produits en réponse à des décharges électriques énergétiques orageuses localisées au-dessous. Pendant les campagnes d'observation EuroSprite, quelques centaines d'images de sprites ont été obtenues, fournissant des informations sur la morphologie, la localisation et le moment de leur production. Des données issues de radars météorologiques, de satellite météosat, de deux types de système de détection d'éclairs, et de récepteur radio large bande ont été analysées. Des études de cas et une étude statistique sur un grand nombre de cas de sprites produits par 7 orages distincts sont réalisées. L'analyse porte sur le rôle de la composante intranuage des éclairs nuage-sol positifs à l'origine des sprites et notamment le lien avec leur morphologie, sur la relation avec le stade d'évolution des orages, et enfin sur les conditions associées à la production d'un jet géant aux Etats-Unis. Les sprites observés ont été produits par des systèmes convectifs de moyenne échelle (MCS) lorsque la partie stratiforme était en phase d'expansion. Les séquences des éclairs nuage-sol et l'activité intranuage observées au moment des sprites confirment une propagation horizontale importante (convective-vers-stratiforme). Les sprites de type colonne sont produits avec des délais plus courts que les sprites de type carotte. Plus le délai est court plus le nombre d'éléments est grand et plus leur luminosité est concentrée à une altitude élevée. Le jet géant semble avoir été favorisé par la configuration de charge et l'activité d'éclairs plutôt que l'altitude du sommet du nuage.This dissertation is devoted to the description of the conditions of production of transient luminous phenomena (sprites, jets, elves) in the mesosphere, which occur in response to energetic lightning discharges in thunderstorms underneath. During EuroSprite observation campaigns, a few hundred images of sprites have been obtained, providing information about event morphology, location and timing. Precipitation data from weather radar and cloud top altitude from Meteosat, as well as two lightning detection networks and a wide-band radio receiver have been analyzed. The methodology includes case studies and a statistical study over a large number of sprites produced by 7 different storms. The work focuses on the aspect of the intracloud lightning component associated with positive cloud-to-ground flashes, the link with the morphology of sprites, and the life cycle of thunderstorm systems. Additionally, a storm which produced a rare gigantic jet observed in the United States is analyzed in detail. The observed sprites were produced by mesoscale convective systems (MCS) during the expanding phase of the stratiform region. The cloud-to-ground flash sequences and the intracloud lightning component observed at the time of sprites confirm a large horizontal convective-to-stratiform propagation, as mechanism of charge collection, explaining displaced sprites. Sprites of column-type are produced with shorter delays than carrot sprites, and the shorter the delay, the more elements, their luminosity concentrating at greater altitudes. The gigantic jet appears to have been promoted by a certain charge configuration and lightning activity pattern, rather than a high cloud top altitude

A distinct negative leader propagation mode

The common phenomenon of lightning still harbors many secrets such as what are the conditions for lightning initiation and what is driving the discharge to propagate over several tens of kilometers through the atmosphere forming conducting ionized channels called leaders. Since lightning is an electric discharge phenomenon, there are positively and negatively charged leaders. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily build for radio-astronomy observations. It is observed that a negative leader rather suddenly changes, for a few milliseconds, into a mode where it radiates 100 times more VHF power than typical negative leaders after which it spawns a large number of more typical negative leaders. This mode occurs during the initial stage, soon after initiation, of all lightning flashes we have mapped (about 25). For some flashes this mode occurs also well after initiation and we show one case where it is triggered twice, some 100 ms apart. We postulate that this is indicative of a small (order of 5 km2) high charge pocket. Lightning thus appears to be initiated exclusively in the vicinity of such a small but dense charge pocket

Numerical Modeling Of Lightning Initiation And Stepped Leader Propagation

Initial breakdown pulses (IBPs) observed at the beginning of cloud-to-ground (CG) lightning flashes and stepped leaders that folloIBPs were modeled using multi-sensor electric field change (E-change) measurements. This study uses data collected with a network of ten E-change sensors located at Kennedy Space Center. Locations (x,y,z,t) of IBPs were found using a time-of-arrival technique called PBFA. Location errors were determined from Monte Carlo simulations and were usually less than 100 m for horizontal coordinates and several hundreds of meters for altitude. Comparison of PBFA source locations to locations from a VHF lightning mapping system shows that PBFA locates most of the `classic\u27 IBPs while the VHF system locates only a few percent of them. As the flash develops during the IB stage, PBFA and the VHF system obtain similar locations when they detect the same IBPs. PBFA also can reliably locate the IBPs of intra-cloud flashes and return stroke (RS) locations. PBFA locations were used as constraints to model six \u27classic\u27 IBPs using three modified transmission line (MTL) models (MTLL--linearly decaying current, MTLE—exponentially decaying current, MTLEI—exponentially increasing current) from the literature and a new model, MTLK, with the current following the Kumaraswami distribution. All four models did a good job of modeling all six IBPs; the MTLE model was most often the best fit. It is important to note that for a given pulse, there is good agreement between the different models on a number of parameters: current risetime, current falltime, two current shape factors, current propagation speed, and the IBP charge moment change. Ranges and mean values of physical quantities found are: current risetime [4.8–25, (13±6)] microseconds, current falltime [15–37, (25±6)] microseconds, current speed [0.78–1.8, (1.3±0.3)]×10 8 m/s (excluding one extreme case of MTLEI), channel length [0.20–1.6, (0.6±0.3)] km, charge moment [0.015–0.30, (0.12±0.10)] C km, peak current [16–404, (80±80)] kA , and absolute average line charge density [0.11–4.7, (0.90±0.90)] mC/m. Currents in the MTLL and MTLE models deposit negative charge along their paths and the mean total charges deposited (Qtot) were -0.35 and -0.71 C. MTLEI currents effectively deposited positive charge along their paths with Qtot = 1.3 C. MTLK is more special regarding how it handles the charges. Initially, along the lower current path, negative charge is deposited and positive charge is deposited onto its upper path making the overall charge transfer almost zero, (Qtot = 3.8×10 -5). Because of this the MTLK model apparently obeys conservation of charge (without making that a model constraint). Two stepped leaders were modeled to match multiple E-change measurements. Time evolution and 2-D locations of stepped leaders were obtained from data collected with a high-speed video camera operated at 50,000 frames/s. The Lu et al. 2011 TDMD (time dependent multidipole) model was used with some modifications. Negative charges were deposited at stepped leader tips based on measured light intensity, and positive charges were deposited at PBFA/LDAR2 locations of IBPs where the stepped leaders probably started. The method has unique advantage of obtaining locations of CG stepped leaders including its branches, unlike previous studies that used simpler paths. Some physical quantities calculated for both stepped leaders: average line charge density = -1.49 and -0.813 mC/m, average current = 0.39 and 0.38 kA, average 2-D stepped leader speed 2.67 and 4.8×105 m/s. These quantities are in excellent agreement with previous studies

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave propagation in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfven waves and particle precipitation related to solar and magnetospheric processes. We review in situ ionospheric processes as well as surface and space weather phenomena that drive troposphere-ionosphere dynamics. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. We also briefly revisit ionospheric irregularities such as spread-F and explosive spread-F, sporadic-E, traveling ionospheric disturbances, Trimpi effect, and hiss and plasma turbulence. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and solving inverse problems and summarize in a final section a few challenging subjects that are important for a better understanding of tropospheric-ionospheric coupling mechanisms

Evaluation of Geostationary Lightning Mapper performance using the Colombia-Lightning Mapping Array

The Geostationary Lightning Mapper (GLM) on the Geostationary Operational Environmental Satellites - R (GOES-R) series satellites is the first operational lightning mapper flown in a geostationary orbit, which provides continuous observations of lightning. In order to make use of these data for improving nowcasting of severe weather and for data assimilation, it is important to characterize and understand the detection capabilities of GLM. Observations from 3-dimensional VHF Colombia Lightning Mapping Arrays (COL-LMA) provide a valuable basis for evaluating the spatial accuracy and detection efficiencies of observations from the recently launched, optical-based Geosynchronous Lightning Mapper (GLM). This Bachelor Final Thesis results of comparing spatially and temporally the individual event (pixel) level for sets of individual discharges from the LMA and GLM observations. The focus is on a representative sample of case studies encompassing different forms of convective organization at different times of day and night. The detection efficiency of GLM relative to LMA will be characterized in terms of the flash number, size, power and height among others

Doctor of Philosophy

dissertationThe optical properties of lightning observed by the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite between 1998 and 2010 are described and examined in the context of how they interrelate, when and where they occur globally, the nature of the cloud environment they illuminate, and the properties of the parent thunderstorm. Daytime (nighttime) flashes that occur over the open ocean are shown to be 31.7% (39.8%) larger and 55.2% (75.1%) brighter than flashes over land. Three factors are proposed that determine the size of the illuminated region: the brightness of the flash, the scattering properties of the cloud medium, and the structure of the electrical breakdown. Some of these results are explored using a Monte-Carlo radiative transfer model. The properties of TRMM Radar Precipitation Features (RPFs) that produce exceptionally large, long-lasting, and optically bright lightning flashes are compared to typical storms. RPFs over land with exceptionally large lightning flashes are up to three times larger than typical RPF thunderstorms and are considerably stronger. Coastal and oceanic RPFs with exceptionally large lightning flashes, as well as RPFs with exceptionally long lasting or bright flashes are also considerably larger and stronger than typical thunderstorms. Finally, high-altitude aircraft passive microwave and electric field observations taken by the NASA ER-2 over the course of multiple field campaigns are used to examine relationships between the properties of electrified clouds and above-cloud electric fields. A retrieval algorithm is created that is capable of estimating above-cloud electric fields from 85 GHz or 37 GHz passive microwave observations. The 37 GHz estimates are only valid over land since the ocean surface appears "cold" at 37 GHz and can reproduce the observed electric fields to within a factor of two 60% of the time. By comparison, the 85 GHz estimates fall within a factor of two of observations more than 70% of the time over land, but the 85 GHz routine is valid for both land and ocean cases. Individual cases are examined, and methods for improving the routine before applying it to satellite observations to study the Global Electric Circuit are discussed

Corona discharges from grounded rods and 337/777 nm emissions of laboratory long sparks

Tesi en modalitat de compendi de publicacions, amb menció internacionalThis thesis presents an investigation on the signatures of corona discharges from grounded rods under thunderstorms and in the laboratory, with optical detections in the 337/777 nm wavelengths for high voltage sparks. This PhD project is contextualized in the European program: Science and Innovation with thunderstorms (SAINT), funded by the Horizon 2020 / Marie Sklodowska Curie Action (Grant agreement ID: 722337). Under conditions of electrification, charged clouds produce an enhancement of the electric field at the ground level. That, in turn, can lead to corona discharges that produce a space charge layer in the vicinity of grounded structures. The study of this phenomenon is useful for the understanding of lightning-related processes and attachment. In addition to the electrical current obtained from the discharges, another important variable is the optical signature generated by the plasma channels. Emissions in many spectra lines associated with reactions of streamers and leaders with the main components of the atmosphere are relevant for visual observations. This work presents a chapter for current literature review of the processes associated with lightning and the main concepts applied. Then, a detailed description of the instrumentation available for the tests carried out in the laboratory and in the field is provided. The first article of this compendium presents data obtained with experiments of a grounded rod under high background electric field in the laboratory and the field. A limited number of works in the literature have presented such data. An analysis correlating pulse frequency, electric field level and average wind speed is the main novelty of the article. A congress paper annexed in the thesis complements the findings comparing the discharges observed at two other experimental sites. The second article describes a compilation of results obtained in the laboratory for investigating optical signatures in two specific lines of the spectra (337 nm and 777 nm), the ones with stronger emissions in lightning-like events. There is special relevance of such experiments for supporting satellite-based observations of lightning by the Atmosphere-Space Interactions Monitor (ASIM) that perform optical measurements in the same wavelength ranges and the operational lightning imagers such as Geostationary Lightning Mapper (GLM) and the future Meteosat Third Generation Lightning Imager (MTG-LI). The conclusions are presented, together with the prospects for future work following the original results achieved with this PhD. This thesis ends with a detailed description of the dissemination activities (presentation at seminars and conferences, coauthored publications in journals and at conferences) and training activities received throughout this project. Finally, the appendix present additional developments and applications of the sensor developed during this doctorate, comprising experiments performed during a two-month internship at the Eindhoven University of Technology (TU/e), and one section with results for the use of photometers to determine the initiation of an upward leader. Such experiments are particularly interesting for understanding space charge production and in the validation of lightning rods. The concepts applied to the development of a corona discharge current sensor were patented together with Dena Desarrollos, the company where the investigations were carried out during this doctorate.Esta tesis presenta una investigación sobre las huellas de descargas de corona en pararrayos durante tormentas eléctricas y en el laboratorio, con detecciones ópticas en las longitudes de onda de 337/777 nm para descargas de alto voltaje. Este proyecto de doctorado se contextualiza en el programa europeo: Science and Innovation with thunderstorms (SAINT), financiado por la Acción Horizon 2020 / Marie Sklodowska Curie (Acuerdo de subvención ID: 722337). En condiciones de electrificación, las nubes cargadas producen un aumento del campo eléctrico a nivel del suelo. Eso, a su vez, puede ocasionar descargas de corona que producen una capa de carga espacial en las proximidades de las estructuras conectadas a tierra. El estudio de este fenómeno es útil para comprender los procesos y la conexión de los canales de los rayos. Además de la corriente eléctrica obtenida de las descargas, otra variable importante es la huella óptica (las señales ópticas a lo largo del tiempo) generada por los canales de plasma. Las emisiones en muchas líneas espectrales asociadas con reacciones de streamers y líderes con los componentes principales de la atmósfera son relevantes para las observaciones visuales. Este trabajo presenta un capítulo de revisión de la literatura actual sobre los procesos asociados a las descargas atmosféricas y los principales conceptos aplicados. A continuación, se realiza una descripción detallada de la instrumentación disponible para las pruebas realizadas en laboratorio y en campo. El primer artículo de este compendio presenta datos obtenidos con experimentos de una varilla puesta a tierra sujeta a un campo eléctrico de fondo elevado en laboratorio y en campo. Un número limitado de trabajos en la literatura han presentado dichos datos. Un análisis que correlaciona la frecuencia del pulso, el nivel del campo eléctrico y la velocidad media del viento es la principal novedad del artículo. Un artículo presentado en congreso adjunto a la tesis complementa los resultados y realiza una comparación de las descargas observadas en otros dos sitios experimentales. El segundo artículo presenta una recopilación de resultados obtenidos en el laboratorio para la investigación de la huella óptica en dos líneas específicas de los espectros (337 nm y 777 nm), las que tienen emisiones más intensas en los rayos. Existe una relevancia especial de dichos experimentos para respaldar las observaciones de rayos basadas en satélites por el Monitor de Interacciones Atmosfera-Espacio (ASIM) que realiza mediciones ópticas en los mismos rangos de longitud de onda y los generadores de imágenes de rayos operacionales como Geostationary Lightning Mapper (GLM) y el futuro Meteosat Third Generation Lightning Imager (MTG-LI). Se presentan las conclusiones, junto con las perspectivas de trabajo futuro siguiendo los resultados originales alcanzados con este doctorado. Esta tesis finaliza con una descripción detallada de las actividades de difusión (presentación en seminarios y congresos, publicaciones en coautoría en revistas y congresos) y actividades formativas recibidas a lo largo de este proyecto. Finalmente, el apéndice presenta desarrollos y aplicaciones adicionales del sensor desarrollado durante este doctorado, que comprende experimentos realizados durante período de prácticas de dos meses en la Universidad Tecnológica de Eindhoven (TU/e), y un apartado con resultados para el uso de fotómetros para determinar la iniciación de un líder ascendente. Estos experimentos son particularmente interesantes para comprender la producción de cargas espaciales y en la validación de pararrayos. Los conceptos aplicados al desarrollo del sensor de corriente de descarga corona fueron patentados junto con Dena Desarrollos, empresa donde se llevaron a cabo las investigaciones durante este doctorado.Postprint (published version

The Development of a New Lightning-Frequency Parameterization and its Implementation in a Weather Prediction Model

Based on a straightforward physical model, a new lightning parameterization has been developed: A two-plate capacitor represents the basic dipole charge structure of a thunderstorm, which is charged by the generator current and discharged by lightning. In this approach, the generator current as well as the discharge strength are parameterized using the graupel-mass field. If these two quantities are known, and if the charging and discharging are in equilibrium, then the flash rate is uniquely determined. This approach remedies shortcomings of earlier theoretical approaches that relate the flash rate e.g., to generator power. No distinction is made between intracloud and cloud-to-ground discharges. In order to test this approach, polarimetric radar data were used, from which the graupel distribution in observed thunderstorms could be inferred. The lightning activity was detected using the LINET network. The comparison between theoretically-predicted and measured flash rates is encouraging: Over a wide range of flash rates, the theoretical approach yields accurate results for isolated thunderstorms. Two existing parameterizations, which only use the depth of the clouds as predictor, produce substantially less accurate forecasts. These two existing approaches, the one developed in this study, as well as a fourth one based on updraft velocity, were implemented in the convection-resolving COSMO-DE numerical weather prediction model. With this model, real-world convective scenarios were simulated. The output of the lightning scheme includes the location and time of every simulated discharge. Testing the performance of the parameterizations with modeled convection is difficult as there is no one-to-one correspondence between observed and modeled convective clouds. Where a comparison between modeled and observed flash rates of individual clouds was possible, the results for individual cells were promising. The comparison of the bulk lightning activity over an area comprising southern Germany and adjacent countries suggests that none of the four parameterizations captures the overall lightning activity well. This is mainly because COSMO-DE does not simulate the observed number of cells at the correct times