Title: Lightning-Related Electromagnetic Wave Phenomena in the Earth's Magnetosphere Author: Jan Záhlava Department: Department of Surface and Plasma Physics Supervisor: doc. RNDr. František Němec, PhD., Department of Surface and Plasma Physics Abstract: The thesis focuses on lightning-related electromagnetic wave phenomena observed by spacecraft in the Earth's inner magnetosphere. Two different approaches are used to identify the frequency and spatial extent where lightning generated emissions significantly contribute to the overall wave intensity. First, whistler detections onboard the DEMETER spacecraft are used to sort the measurements according to the whistler activity. Second, we use a geographic distribution of lightning activity and analyze a dependence of the overall wave intensity on geomagnetic longitude. We show that, especially during the night, the overall wave intensity observed in the plasmasphere is well correlated with lightning activity. The other focus of the study is on special electromagnetic wave events consisting of alternating frequency bands of enhanced and reduced wave intensity formed in the ionosphere due to lightning. We analyze their occurrence and parameters, and we suggest a possible mechanism of their formation. Keywords: lightning, waves in plasma, whistlers, plasmasphere

I takt med att e-handeln växer sig större behöver fysiska butiker blir allt mer upplevelseinriktad och leverera unika kundupplevelser för att inte mista sina kunder. Ljus och belysning är en viktig komponent för att påverka kundupplevelse, eftersom ljus direkt påverkar komfort och navigering i butiken. För att skräddarsy belysning för en specifik butik krävs expertis från en ljusdesigner. Finjusteringar av belysning på plats i butiken kan dock vara en utmaning även för ljusdesigners på grund av tidsbegränsning, mängden fel som kan uppstå i ljusinstallationen och avsaknaden av effektiva verktyg för att justera olika aspekter av ljus. Denna studie syftar till att förstå om ett mobilt verktyg för att justera ljusets färgtemperatur i realtid kan hjälpa en ljusdesigner vid installationen av belysning i en butik. För att förstå de utmaningar som är involverade i ljusdesigners arbete har två metoder använts. En deltagande observationsstudie och semistrukturerade intervjuer med tre ljusdesigners. Med kunskap från dessa metoder utfördes ett användarstudie där två versioner av en mobilapplikation för justera ljus testades. Detta utfördes för att dels undersöka användningen av en befintlig applikation och för att identifiera vilka element i den här typen av verktyg som är viktiga för en ljusdesigner. Denna studie indikerade att ett sådant mobilverktyg kan vara mycket användbart, men endast om det innehåller alla nödvändiga element som behövs för att finjustera en ljusinstallation. Studien visade även att en av de viktigaste komponenterna av ett sådant mobilt verktyg är möjligheten att justera färgtemperaturen på ljus, särskilt när man skapar belysning specifikt för en butik. En designövning utfördes för att undersöka hur användbara befintliga verktyg för att justera färgtemperatur är och hur sådana verktyg kan utformas för att passa en ljusdesigners behov. Baserat på resultatet av denna övning skapades en prototyp på ett verktyg för att justera färgtemperaturen av ljus. Denna prototyp utvärderades genom en formativ användarstudie samt ett frågeformulär för att utvärdera ett systems användbarhet. Enligt resultatet av testet uppfattades prototypen vara användbar. Sammantaget tyder resultaten från denna studie på att det finns ett behov av denna typ av mobila verktyg som effektivt kan hjälpa ljusdesigner i deras arbete. / With the significant growth of e-commerce, physical stores need to become more experience-driven, and delivering unique, high impact customer experiences is a core for their success. Lighting is an important element of customer experience, as it directly affects comfort and navigation. In order to customize lighting for a store,expertise from a light designer is needed. However, on-site lighting fine tuning is a challenge due to time restrictions, amount of error occurring to the light installation, and easy accessible tools for adjustments. This study aims to understand whether an mobile tool for adjusting color temperature of lights in realtime can assist a light designer when installing a light installation in a retail store. To understand the challenges involved in the work of lightning designers, two methods have been used. A participatory observational study and semistructured interviews with three light designers. Given that, an exploratory user test was performed, testing two versions of a lighting manager application in order to investigate the usage of an existing application and what elements in this kind of tool are of most importance for a light designer. The user tests indicated that a mobile tool like this could be very useful, but only if it contains all the necessary elements needed. The results show that one of the essential elements of such a tool regards options for adjusting color temperature, when creating specifically for a retail store. In order to investigate further how useful existing light color temperature tools are and how they could be designed to suit a light designer needs, a design exercise was performed. Through the result of this exercise a prototype of a color temperature tool was created. This prototype was evaluated through a formative user study. The usability of the prototype was evaluated through a System usability score evaluation questionnaire. According to the test, the prototype was found to be usable. All in all, the results of this study indicate that there is a need for this kind of mobile tools that can effectively assist light designers in their work.

Det akademiska biblioteket utgör en viktig del av studentens studietid som en tillhandahållare av vetenskaplig litteratur. De senaste decenniernas digitalisering har förändrat biblioteket i grunden. I takt med att mer tryckt material övergår i elektronisk form i databaser blir beroendet av fysiska medier mindre. Intresset för uppgiften har sin förankring i att balansera detta förhållande genom en lukrativ gestaltning av det fysiska studierummet. Det skall vara en plats som bidrar till att studenter känner sig såväl avslappnade som motiverade för att fullfölja sina skoluppgifter. En implementering av detta gjordes i form av ett ombyggnadsförslag för utbildningen Byggteknik & Designs befintliga lokaler på Kungliga Teknisk Högskolan.  I samband med utredningen om hur dagens akademiska bibliotek ser ut besöktes ett antal sådana i Stockholmsområdet med intervjuer bland personal. Vid studiebesöken undersöktes principiella frågor som rör studiemiljön, ombyggnader och studenters beteendemönster. Sådan information tillät oss att identifiera vissa av biblioteksmiljöns problemområden, för att därefter kunna lösa dessa.  Med användning av gällande riktlinjer och standarder utarbetades en arbetsmiljö som ger rätt förutsättningar för aktivitetsbaserade studier. Det gäller exempelvis noggrann planering av artificiell ljussättning. Likaså var förhållning till naturligt ljus viktig, och genom Svensk standardkrav för dagsljusinsläpp kunde dess inverkan på bibliotekslokalen kontrolleras. Detta är exempel på arbetet med att utnyttja och förbättra lokalens egenskaper ur ett arkitektoniskt perspektiv. / The academic library is an important aspect of a students education as it contributes to providing scientific literature. Contemporary society has led to the digitalisation of educational media. Consequently, libraries are becoming more reliant upon the usage of electronic databases as opposed to the usage of printed materials. The interest in the task is rooted in our desire to create an environment where students feel both relaxed and motivated to carry out educational tasks. An implementation of this was done in the form of a rebuilding proposal for the Building Engineering and Design existing facilities of Royal Institute of Technology. Our investigation consisted of conducting interviews with staff members from a variety of academic libraries in Stockholm area to gain a useful insight upon the concerns and fundamental issues which many of these members have. Such information allowed us to identify problems in regards to library settings and thereafter overcome it. Using current guidelines and standards, a work environment was developed that provides the right conditions for activity-based studies. This applies, for example, to careful planning of artificial light. The relation to natural light was also important, and by Swedish standard requirements for daylight emitting, its influence on the library room could be controlled. Thus we see an example of utilizing and improving the characteristics of the facility from an architectural perspective.

This work is devoted to the computational modeling of a lightning strike electric arc discharge induced air plasma and the material response under the lightning strike impact. The simulation of the lightning arc plasma has been performed with Finite element analysis in COMSOL Multiphysics. The plasma is regarded as a continuous medium of a thermally and electrically conductive fluid. The electrode mediums, namely the cathode and anode, have also been included in the simulation in a unified manner, meaning that the plasma and electrode domains are simulated concurrently in one numerical model. The aim is to predict the lightning current density, and the heat flux impinged into the anode's material surface, as well as the lightning arc expansion and pressure and velocity of the plasma flow. Our predictions have been validated by the existing experimental data and other numerical predictions reported by former authors.

No description available.

<p>  </p> <p>Rapid intensification of low-level rotation in non-classic tornadic storms in southeastern United States, often at time scales shorter than the volume updates from existing opera- tional radars, calls for a deeper understanding of storm-scale processes. There is growing evidence that the highly nonlinear interactions between vertical wind shear and cold pools regulate the intensity of downdrafts, low- and mid-level updrafts, and thus tornadic poten- tial in supercells. Tornado-strength circulations are more likely associated with cold pools of intermediate strength. The microphysical pathway leading to storm electrification also plays a major role in the regulation of cold pool intensity. Storm electrification and subsequent lightning initiation are a by-product of charging of ice hydrometeors in the mixed-phase updrafts. Lightning flashes frequently initiate along the periphery of turbulent updrafts and total flash rate is controlled by the updraft speed and volume.</p> <p><br></p> <p>In the first part of this work, polarimetric fingerprints like ZDR and KDP columns (proxies for mixed-phase updraft strength) are objectively identified to track rapid fluctuations in updraft intensity. We quantify the volume of ZDR and KDP columns to evaluate their utility in predicting temporal variability in lightning flash characteristics and the onset of severe weather. Using observational data from KTLX radar and Oklahoma Lightning Mapping Array, we had previously found evidence of temporal covariance between ZDR column volume and the total lightning flash rate in a tornadic supercell in Oklahoma. </p> <p><br></p> <p> Here, we extend our analysis to three high-shear low-CAPE (HSLC) cases observed during the 2016-17 VORTEX-SE field campaign in Northern Alabama. In all three scenarios (one tornadic and one nontornadic supercell, and a quasi-linear convective system), the KDP column volume had a stronger correlation with total flash rates than the ZDR column volume. We also found that all three storms maintained a normal tripole charge structure, with majority of the cloud-to-ground (CG) strikes lowering negative charge to the ground. The tornadic storm’s CG polarity changed from negative to positive at the same time it entered a region with higher surface equivalent potential temperature. In contrast to the Oklahoma storm, lightning flash initiations in HSLC storms occurred primarily outside the footprint of ZDR and KDP column objects.</p> <p><br></p> <p>Storm dynamics coupled with microphysical processes such as diabatic heating/cooling and advection/sedimentation of hydrometeors also plays a significant role in electrification of thunderstorms. Simulation of deep convection, therefore, needs to account for the feedback of microphysics to storm dynamics. In the second part of this work, the NSSL microphysics scheme is used to simulate ice mass fluxes, cold pool intensity, and noninductive charging rates. The scheme is run in its triple-moment configuration in order to provide a more realis- tic size-sorting process that avoids pathologies that arise in double-moment representations.</p> <p><br></p> <p>We examine the possible tertiary linkage between noninductive charging rates and cold pool through their dependence on mixed-phase microphysical processes. The Advanced Re- gional Prediction System (ARPS) model is used to simulate the same three HSLC cases from VORTEX-SE 2016-17 IOPs. WSR-88D radar reflectivity and Doppler velocity observations are assimilated in a 40-member ensemble using an ensemble Kalman filter (EnKF) filter.</p> <p><br></p> <p>In all three cases, the simulated charge separation is consistent with the observed normal tripole. Greater updraft mass flux, supercooled liquid water concentration, and nonprecip- itation mass flux explain the nontornadic supercell’s higher total flash rate compared to the tornadic supercell. Positive and negative graupel charging rates were found to have the greatest linear correlation with updraft mass flux, followed by precipitation mass flux in all three cases. At zero time lag, horizontal buoyancy gradients associated with a surface cold pool were not found to be correlated with either the charging rates or the updraft and precipitation mass flux. Total flash rate based on empirical relationships between simulated ice mass fluxes was lower than the observed values.</p>

Thunderstorms, due to their high frequency of occurrence over southern Africa, and their major contribution to summer rainfall are the primary focus of very short range forecasting and nowcasting efforts in South Africa. With a limited number of surface and upper-air observations and the limited availability of numerical model output most southern African countries are heavily reliant on satellite technology. In developing tools for the first twelve forecast hours the South African Weather Service has to address both the national and regional needs. Thus, the blending of techniques in an optimal manner is essential. This study initially describes how the Global Instability Index product derived from the European Meteosat Second Generation Satellite was adapted for South African circumstances using a different numerical model to provide background information – creating the Regional Instability Indices (RII). The focus of the study is the development of a new convection indicator, called the Combined Instability Index (CII), which calculates the probability of convection from satellite derived instability indices and moisture, as well as height above sea level early in the morning when the sky is relatively cloud free. Early morning CII values were evaluated statistically against the occurrence of lightning over South Africa, where a lightning network is available, as well as against satellite derived precipitation over southern Africa, later in the same day. It is shown that the CII not only performs well, but also outperforms the individual RII when compared to the occurrence of lightning. The CII will be beneficial to operational forecasters to focus their attention on the area which is most favourable for the development of convection later in the day. / Environmental Sciences / Ph. D. (Environmental Sciences)

As linhas de distribuição de energia estão freqüentemente expostas a sobretensões causadas por descargas atmosféricas diretas e indiretas. As formas de onda dessas sobretensões têm uma faixa de variação muito ampla e podem diferir bastante do impulso atmosférico normalizado utilizado em ensaios para verificação da adequação dos projetos das isolações dos equipamentos frente a sobretensões atmosféricas (1,2 / 50 microssegundos). É fato conhecido que a suportabilidade das isolações depende não só da amplitude como da forma de onda das solicitações. Diferentes modelos têm sido propostos para se estimar o desempenho das isolações frente a impulsos não normalizados, sendo o modelo do efeito disruptivo (disruptive effect model) um dos mais utilizados. Existem, contudo, diferentes métodos de aplicação desse modelo, ou seja, diferentes formas de se estimar os parâmetros necessários para a sua aplicação. Este trabalho visa avaliar o comportamento dielétrico de isoladores de média tensão e analisar os principais métodos para estimativa da suportabilidade desses equipamentos frente a sobretensões atmosféricas com formas de onda diferentes da normalizada. Para essa avaliação foram realizados ensaios em um isolador tipo pino, de porcelana, com tensão nominal de 15 kV, nos quais foram utilizadas, além do impulso atmosférico normalizado, outras ondas selecionadas com base em resultados de medição e de cálculo. Modificações realizadas no circuito de um gerador de impulsos de alta tensão convencional permitiram a geração de tensões com formas de onda bastante semelhantes às de sobretensões induzidas por descargas atmosféricas tanto em linhas de tamanho natural como em experimentos realizados com modelo reduzido. São apresentados e discutidos os resultados dos ensaios de tensão disruptiva de impulso atmosférico a 50 % e as curvas tensão-tempo (U x t) obtidas para cada impulso, considerando ambas as polaridades. A avaliação dos métodos de aplicação do modelo do efeito disruptivo foi realizada com base em comparações entre as curvas tensão-tempo obtidas nos ensaios e as curvas previstas por cada modelo, para cada uma das ondas selecionadas. / Overhead distribution lines are often exposed to lightning overvoltages, whose waveshapes vary widely and can differ substantially from the standard impulse voltage waveshape used to test electric equipment insulation against lightning surges (1.2 / 50 microseconds wave). It is well known that the voltage withstand capability of insulation depends not only on the amplitude but also on the voltage waveshape. Different models have been proposed for predicting the strength of insulation subjected to impulses of non-standard waveshapes. One of the most commonly used is the \"disruptive effect model\". There are, however, different methods of applying this model, that is, different ways of estimating the parameters needed for its application. This thesis aims at evaluating the dielectric behavior of medium voltage insulators subjected to impulses of non-standard waveshapes, as well as at evaluating the main methods for predicting their dielectric strength against such impulses. For the analysis, tests were performed on a pin type porcelain insulator with rated voltage of 15 kV, using, besides the standard lightning impulse voltage waveshape, other s waveshapes selected based on the characteristics of measured and calculated lightning overvoltages. Modifications made to the circuit of a conventional impulse voltage generator allowed to obtain voltage waveshapes very similar to those of lightning-induced voltages measured in experiments conducted both in lines of natural size and in reduced model. The test results relative to the critical lightning impulse flashover voltage (U50) and the volt-time characteristics obtained for the positive and negative polarities of each waveshape are presented and discussed. The evaluation of the methods of determining the parameters of the disruptive effect model was based on comparisons between the volt-time curves obtained from the laboratory tests and those predicted by each method, for each of the selected voltage waveshapes.

<p>This thesis deals with the electromagnetic compatibility (EMC) problems of distributed electrical networks, especially that caused by lightning to electrified railway. Lightning transients were found to damage important devices that control train movements, causing traffic stoppage and delays. This thesis attempts to develop computational models for identification of parameters influencing the coupling phenomena between those devices and lightning. Some supporting experimental investigations are also carried out. This thesis forms the groundwork on the subject of lightning interaction with the electrified railway networks.</p><p>Lightning induces transient overvoltages in railway conductor systems such as tracks, overhead wires, and underground cables, either due to direct lightning strike to the system or due to the coupling of electromagnetic fields from remote strikes. Models based on multiconductor transmission line theory were developed for calculating the induced voltages and currents. A transmission line return stroke model, that can predict the remote electromagnetic fields comparable to experimental observations, is also developed. </p><p>Earlier works on modeling earth return impedances for transient studies in power distribution systems are not readily applicable for railways for lightning transients, in cases of low earth conductivities found in Sweden and for large variation in conductor heights. For the wires above ground, the ground impedance models were modified for wide range of frequencies, soil conductivities and wide spread of conductor heights. Influences of pole insulator flashovers, pole-footing soil ionizations and interconnections between the conductors on the lightning surge propagation are studied. Wave propagation in buried shielded and unshielded cables with ground return is studied. Simplified, valid and computationally efficient ground impedance expressions for buried and on-ground wires are proposed. A model for the coupling phenomena (transfer impedance) through multiple cable shields with multiconductor core is also proposed. Besides, experimental studies on lightning induced transients entering a railway technical house, failure modes of relay and rectifier units used in the train position/signaling applications for lightning transients are performed. A high frequency circuit model for the booster transformer for lightning interaction studies is developed. The simulation models are being converted to user-friendly software for the practicing engineers of the railway industry.</p>

<p>The present society is highly dependant on complex electronics systems, which have a low damage threshold level. Therefore, there is a high risk of partial or total loss of the system’s electronics when they are exposed to a thunderstorm environment. This calls for a deep understanding on the mechanism related to the interaction of lightning generated electromagnetic fields with various large distributed/scattered systems. To accurately represent the interaction of lightning electromagnetic fields with electrical networks, it is necessary to have return stroke models capable to reproduce the electromagnetic field signatures generated by a lightning flash. Several models have been developed in the recent past to study the field-to-wire coupling mechanism. The most popular, simple and accurate among the available models is the Agrawal et al. model. On the other hand, ATP-EMTP is a well-known transient simulation package widely used by power engineers. This package has various built-in line models like Semlyen, Marti and Noda setups. There is a difficulty in applying the Agrawal et al. model with the built-in line models of ATP-EMTP, as the voltage source due to the horizontal component of electric field in Agrawal et al. model is in series with the line impedance and not in between two transmission line segments. Furthermore, when the electromagnetic field is propagating over a finite conducting ground plane, the soil will selectively attenuate the high frequency content of the electromagnetic field; causing a change in the field wave shape. A finite conducting ground will also produce a horizontal field component at the ground level. Several approximations are available in the literature to obtain the horizontal electric field; namely the wave-tilt and the Cooray-Rubinstein approximation. Consequently, it is important to investigate the change on the induced voltage signature when the power line is located over a finitely conducting ground. Additionally, to provide protection from lightning induced transients it is necessary to use Surge Protective Devices (SPDs) capable of diverting the incoming transients and provide protection level necessary to avoid damage in the equipment. However, standard test procedures of the SPDs do not take into account sub-microsecond structure of the transients. Therefore, to provide the required protection level to sensitive equipments connected to the low voltage power network, it is essential to understand the response of SPDs subjected to high current derivative impulses. This thesis is aimed to investigate the research problems as addressed above. Special attention will be given to a new proposed return stroke model, a simple circuit approach for efficient implementation of Agrawal et al. model using ATP-EMTP, the effect of the soil conductivity on the lightning induced overvoltage signatures and the response of surge protective devices subjected to high current derivative impulses.</p>