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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Observations of solar wind related climate effects in the Northern Hemisphere winter

Maliniemi, V. (Ville) 21 December 2016 (has links)
Abstract This thesis studies the long-term relation between the solar wind driven energetic particle forcing into the atmosphere and the tropospheric circulation in the Northern Hemisphere winter. The work covers the period of more than one hundred years since the turn of the 20th century to present. The thesis makes a statistical analysis of satellite measurements of precipitating energetic electrons, sunspot number data and geomagnetic activity, and compares them with temperature and pressure measurements made at the Earth's surface. Recent results, both observational and from chemistry climate models, have indicated significant effects in the Earth's middle atmosphere due to the energetic electrons precipitating from the magnetosphere. These effects include the formation of reactive hydrogen and nitrogen oxides in the high latitude mesosphere and the depletion of ozone caused by them. Ozone is a radiatively active and important gas, which affects the thermal structure and dynamics of the middle atmosphere. Accordingly, the depletion of ozone can intensify the large scale stratospheric circulation pattern called the polar vortex. Winter weather conditions on the surface have been shown to be dependent on the polar vortex strength. This thesis shows that there is a significant relation between the average fluxes of medium energy (ten to hundred keVs) precipitating electrons and surface temperatures in parts of the Northern Hemisphere in winter time. Temperatures are positively correlated with electron fluxes in North Eurasia and negatively correlated in Greenland during the period 1980-2010 which is covered by direct satellite observations of precipitating particles. This difference is especially notable when major sudden stratospheric warmings and the quasi-biennial oscillation (QBO), which both are known to affect the polar vortex strength, are taken into account. When extended to the late 19th century, the analysis shows that a similar temperature pattern is predominated during the declining phase of the sunspot cycle. The high speed solar wind streams and energetic particle precipitation typically maximize also at the declining phase of the solar cycle. This specific temperature pattern is related to the variability of the northern annular mode (NAM), which is the most significant circulation pattern in the Northern Hemisphere winter. Before the space era, geomagnetic activity measured by ground observations can be used as a proxy for energetic particle precipitation. Earlier studies have found a significant positive correlation between geomagnetic activity and NAM since the 1960s. We find that, when the QBO measured at 30 hPa height is in the easterly phase, a positive correlation is extended to the beginning of 1900s. We also show that high geomagnetic activity causes a stronger effect in the Northern Hemisphere winter than high sunspot activity, especially in the Atlantic and Eurasia. A comprehensive knowledge of the Earth's climate system and all its drivers is crucial for the future projection of climate. Solar variability effects have been estimated to produce only a small factor to the global climate change. However, there is increasing evidence, including the results presented in this thesis, that the different forms of solar variability can have a substantial effect to regional and seasonal climate variability. With this new evidence, the solar wind related particle effects in the atmosphere are now gaining increasing attention. These effects will soon be included in the next coupled model inter comparison project (CMIP6) as an additional solar related climate effect. This emphasizes the relevance of this thesis.
92

Etude des systèmes binaires galactiques à très haute energie avec HESS et HESS-II / Study of galactic binary systems at very high energy with H.E.S.S. and H.E.S.S. II

Mariaud, Christian 25 May 2018 (has links)
En astronomie gamma, les systèmes binaires sont des objets stellaires impliquant une étoile massive et un objet compact, le plus léger des deux en orbite autour de l’autre. Ils émettent de façon régulière à haute et très haute énergie (E > 100 GeV) et peuvent être détectés par le réseau de télescopes H.E.S.S.. Malgré leur faible nombre, ils présentent une grande diversité de comportement et sont caractérisés par une modulation de flux dépendant de la position de l’objet compact. 2 systèmes binaires sont étudiés : LS 5039 et PSR B1259–63, en effet un jeu de données conséquent est disponible puisque ces sources sont observées maintenant depuis plus de 10 ans. En 2012, le cinquième télescope de plus grande taille a commencé ses observations et permet ainsi de faire la connexion avec le domaine du GeV.Une modélisation de ces deux systèmes binaires dans le cas d’une diffusion anisotrope inverse Compton dans le régime de Klein–Nishina sera aussi proposée avec une prise en compte du disque circumstellaire pour PSR B1259¡63. Les données recueillies lors d’une observation peuvent être détériorées par une atmosphère dégradée, affectant ainsi le flux de photons ° collectés. Un coefficient traduisant la qualité de l’atmosphère est donc nécessaire. De plus les gerbes peuvent être déformées à cause de laprésence du champ magnétique terrestre, les études de ces phénomènes sont donc nécessaires pour essayer de corriger ces effets. / Binary systems in gamma astronomy are stellar objects involving a massive star with a compact object, the lightest in orbit around the other. They emit regularly at high energy and very high energy (E > 100 GeV) for detection by H.E.S.S. telescopes. Despite their low relative number, they are all characterized by a modulation of gamma photon flux which depends on the position of the lightest object. We will focus more on 2 binary systems : LS 5039 and PSR B1259–63, we have a susbstantial data, H.E.S.S. telescopes have regularly observed these objects for more than 10 years. In 2012, a fifth telescope much larger size, began observations and enables to get events at lower energy and then make the connection with other experiments such as Fermi-LAT. A modelling of these two binary systems in anisotropic inverse Compton in Klein–Nishina regime are also presented and the circumstellar disk is taken into account for PSR B1259–63. Data taken by theH.E.S.S. telescopes can be improved. During observations, atmosphere can be degraded and thus affecting the flux of gamma photons collected. It’s therefore important to know the transparency coefficient of the atmosphere during an analysis. Furthermore, the electromagnetic air showers are more distorted because of the Earth’s magnetic field, a study of these phenomenas is necessary to correct these effects.
93

Definition and evaluation of a system for measuring local geomagnetic variations : Autonomous station for magnetic measurements / Definition och utvärdering av ett system för mätning av lokala geomagnetiska variationer : Autonom station för magnetiska mätningar

Olsson, Viktor January 2023 (has links)
Earth is under constant influence of the Sun and phenomena driven by the solar wind that may affect man-made technology. These events are summarized under the concept of space weather. This creates variations in Earth’s magnetic field and nearby space. Space weather can affect power grids, gas pipelines and also have effects on human health. Due to these effects, as well as the scientific interest in space and the growing space industry, the need to monitor space weather, the space environment and how Earth is affected by them increases. Accurate magnetic mesurements rely on expensive magnetometers and careful calibration. Swedish Institute of Space Physics IRF, operates two magnetometers in Sweden, one observatory and one variometer to measure local geomagnetic variations. For the purpose of space weather, measurements of local variations have high demands on temporal resolution and precision but not the same need for long-term accuracy. The purpose of this thesis is to define and evaluate an autonomous system for local geomagnetic variations, with future hopes of creating a network of systems for space weather monitoring. The future goal is to be able to place systems in remote locations where they will be able to conduct measurements autonomously. The work was done by analysis and testing of a fluxgate magnetometer that was placed close to one of the IRFs existing magnetometers. Using data from the existing station as a reference, an analysis of the magnetometer could be performed. The results showed that the tested magnetometer had less precision than the existing station but could within a certain frequency range provide good results that make it possible to measure the local geomagnetic variations that may be of use for space weather. Conclusions from this study show that it is possible to create a simpler autonomous system for measurements of the local geomagnetic variations, but that this system requires further development, where future work can be based on this degree project as a basis. / Jorden är under konstant påverkan av solen och fenomen drivna av solvinden som kan påverka mänsklig teknologi. Dessa event sammanfattas under begreppet rymdväder. Genom detta skapas variationer i Jordens magnetfält och närliggande rymd. Rymdväder kan påverka kraftnät, gasledningar och även ha effekter på mänsklig hälsa. På grund av dessa effekter samt det vetenskapliga intresset för rymden och den växande rymdbranschen ökar behovet av att övervaka rymdväder, rymdmiljön samt hur Jorden påverkas av de. Exakta magnetiska mätningar är beroende av dyra magnetometrar och nogrann kalibrering. Institutet för Rymdfysik IRF driver två magnetometrar i Sverige, ett observatorium och en variometer för att mäta lokala geomagnetiska variationer. Då mätningar av lokala variationer har höga krav på temporal upplösning och precision men inte samma behov av kontroll på långsiktig noggrannhet. Syftet med det här examensarbetet är att definiera och utvärdera ett autonomt system för lokala geomagnetiska variationer, med framtida förhoppningar om att skapa ett nätverk av system för övervakning av rymdväder. Framtidsmålet är att kunna placera ut system på avlägsna platser där det autonomt ska kunna bedrivas mätningar. Arbetet gjordes genom analys och tester med en fluxgate-magnetometer som placerades i närheten av en av IRF befintliga magnetometrar. Med data från den existerande stationen som referens kunde en analys av magnetometern utföras. Resultatet visade att den testade magnetometern hade mindre precision än den befintliga stationen men kunde inom ett viss frekvensspann förse goda resultat som gjorde det möjligt att mäta de lokala geomagnetiska variationerna som kan vara till nytta för rymdväder. Slutsatser från denna studie visar att det är möjligt att skapa ett enklare autonomt system för mätningar av de lokala geomagnetiska variationerna men att detta system kräver vidare utveckling, där framtida arbete kan utgå från resultaten som erhölls i detta examensarbete.
94

Progress in space weather modeling in an operational environment

Tsagouri, I., Belehaki, A., Bergeot, N., Cid, C., Delouille, V., Egorova, T., Jakowski, N., Kutiev, I., Mikhailov, A., Nunez, M., Pietrella, M., Potapov, A., Qahwaji, Rami S.R., Tulunay, Y., Velinov, P., Viljanen, A. January 2013 (has links)
Yes / This paper aims at providing an overview of latest advances in space weather modeling in an operational environment in Europe, including both the introduction of new models and improvements to existing codes and algorithms that address the broad range of space weather's prediction requirements from the Sun to the Earth. For each case, we consider the model's input data, the output parameters, products or services, its operational status, and whether it is supported by validation results, in order to build a solid basis for future developments. This work is the output of the Sub Group 1.3 "Improvement of operational models'' of the European Cooperation in Science and Technology (COST) Action ES0803 "Developing Space Weather Products and services in Europe'' and therefore this review focuses on the progress achieved by European research teams involved in the action.
95

NATURAL PHENOMENA AS POTENTIAL INFLUENCE ON SOCIAL AND POLITICAL BEHAVIOR: THE EARTH’S MAGNETIC FIELD

East, Jackie R 01 January 2014 (has links)
Researchers use natural phenomena in a number of disciplines to help explain human behavioral outcomes. Research regarding the potential effects of magnetic fields on animal and human behavior indicates that fields could influence outcomes of interest to social scientists. Tests so far have been limited in scope. This work is a preliminary evaluation of whether the earth’s magnetic field influences human behavior it examines the baseline relationship exhibited between geomagnetic readings and a host of social and political outcomes. The emphasis on breadth of topical coverage in these statistical trials, rather than on depth of development for any one model, means that evidence is only suggestive – but geomagnetic readings frequently covary with social and political variables in a fashion that seems inexplicable in the absence of a causal relationship. The pattern often holds up in more-elaborate statistical models. Analysis provides compelling evidence that geomagnetic variables furnish valuable information to models. Many researchers are already aware of potential causal mechanisms that link human behavior to geomagnetic levels and this evidence provides a compelling case for continuing to develop the line of research with in-depth, focused analysis.
96

Análise do campo elétrico atmosférico durante tempo bom e distúrbios geofísicos

Anaya, José Carlos Tacza 19 January 2015 (has links)
Made available in DSpace on 2016-03-15T19:35:52Z (GMT). No. of bitstreams: 1 JOSE CARLOS TACZA ANAYA.pdf: 7682166 bytes, checksum: f3eebed2cf5cb0f5ecda9415f8754978 (MD5) Previous issue date: 2015-01-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / In this dissertation, we present the capability of a new network of sensors to monitor the atmospheric electric field at various locations in South America. The main goal is to obtain the characteristic Universal Time daily curve of the atmospheric electric field in fair-weather. That curve is known as the Carnegie curve, which is related to the currents flowing in the Global Atmospheric Electric Circuit. This has been accomplished using monthly, seasonal and annual averages. After obtaining our standard curve of variation of the electric field in fair-weather, the deviations related to phenomena such as solar flares, solar protons events, geomagnetic storms, total solar eclipse and seismic activity are analyzed and commented. / Neste trabalho de dissertação apresenta-se a capabilidade de uma nova rede de sensores para monitorar o campo elétrico atmosférico em vários locais na América do Sul. O objetivo principal é obter a curva diária do campo elétrico atmosférico de tempo bom. Para isto foram realizadas médias mensais, sazonais e anuais. Essa curva é comparada com a curva característica em Tempo Universal conhecida como a Curva de Carnegie, a qual é relacionada com as correntes fluindo no Circuito Elétrico Atmosférico Global. Depois de obter a curva padrão de variação do campo elétrico atmosférico de tempo bom, foram analisados e comentados os desvios relacionados a explosões solares, eventos de prótons solares, tempestades geomagnéticas, eclipse solar e atividade sísmica.

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