Дисертації з теми "Geomagnetic field variations"
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Turton, Ian. "Temporal and spatial variations of the geomagnetic field, up to a timescale of 10⁵ years." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/11472.
Повний текст джерелаNakano, Shinya. "Variations of large-scale field-aligned currents and their effects on mid-latitude geomagnetic disturbances." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147822.
Повний текст джерелаSaturnino, Diana. "Une méthode d’observatoires virtuels pour décrire les variations temporelles du champ géomagnétique et applications aux mesures de la mission Swarm." Nantes, 2015. https://archive.bu.univ-nantes.fr/pollux/show/show?id=181308db-f221-4fd6-84dc-ccfc2af8e6cd.
Повний текст джерелаLa description des variations temporelles du champ géomagnétique (variation séculaire ou SV) est cruciale pour la compréhension de la dynamo. La SV est connue avec une grande précision dans les observatoires magnétiques, qui ont une répartition spatiale inégale. Les satellites donnent des observations globales du champ et de sa SV. Leurs données sont utilisées par les modèles globaux en harmoniques sphériques. Les petites échelles spatiales de la SV décrites par ces modèles peuvent montrer des erreurs par rapport aux mesures des observatoires. Dans cette étude je tente d'extraire des séries temporelles avec des mesures satellitaires comme dans les observatoires. L'approche des observatoires virtuels (VO) est suivie. Un maillage global de volumes à l'altitude du satellite est défini. Pour cela, la technique des Equivalent Source Dipoles (ESD) est appliquée. Pour chaque VO et intervalle de temps donné, toutes les mesures sont réduites à un endroit unique, menant à des séries temporelles similaires à celles disponibles dans les observatoires à la surface. L’approche est validée avec des donnes synthétiques et puis appliquée aux mesures de la mission Swarm. Les séries temporelles VO-ESD sont comparées à celles à la surface et aux prédictions par un modèle. L'approche décrit correctement les variations temporelles du champ à l'échelle locale. Un maillage global de VO est construit et utilisé pour obtenir des modèles globaux. Les modèles sont capables de décrire l'évolution du champ magnétique à la fois à l'altitude du satellite et à la surface. Toutefois des modélisations plus complexes pourront être faites pour profiter des séries temporelles VO-ESD
Ménabréaz, Lucie. "Production atmosphérique du nucléide cosmogénique 10 Be et variations de l'intensité du champ magnétique terrestre au cours des derniers 800 000 ans." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4316/document.
Повний текст джерелаAmong the methods for reconstructing the geomagnetic field history, studying the variations in cosmogenic isotopes production in the atmosphere has recently developed. At multi millennial scales, this production is mainly modulated by the geomagnetic field intensity. Its record in terrestrial archives provides an independent reading to complement paleomagnetic methods. This work aims at tracing the changes in 10Be production rates recorded in marine sediments, in order to reproduce the geomagnetic variations for the past 800,000 years. Authigenic 10Be/9Be ratios measured using Accelerator Mass Spectrometry along three sequences from different latitudes, characterize the 10Be global production during two time intervals. (1) During the dipole moment low associated with the Laschamp excursion (~ 41,000 years BP), the 10Be overproduction at 38°N and 2°S, confirmed by measurements of 10Be/230Thxs, is identical to that recorded in the Greenland ice sheet. (2) Studying a core collected near the equator and covering the interval 800,000 – 250,000 years BP (Brunhes epoch) reveals the successive phases of global 10Be overproductions triggered by dipole moment lows associated to the Brunhes-Matuyama reversal and also to several other documented excursions. Calibrating these records with absolute values available in the literature allows quantifying dipole moments. These are then compared to paleomagnetic reference reconstructions over the same time series. Bearing out the number and extent of these dipole field lows allows considering to refine their chronology before using their features to get a better understanding of the geodynamo rhythms throughout the last Million years
McArdle, Nicholas John. "Long term variation in geomagnetic field intensity and terrestrial planet development." Thesis, University of Liverpool, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569142.
Повний текст джерелаWardinski, Ingo. "Core surface flow models from decadal and subdecadal secular variation of the main geomagnetic field." Potsdam : Geoforschungszentrum, 2005. http://www.gfz-potsdam.de/bib/pub/str0507/0507.htm.
Повний текст джерелаWardinski, Ingo. "Core surface flow models from decadal and subdecadal secular variation of the main geomagnetic field." [S.l.] : [s.n.], 2004. http://www.diss.fu-berlin.de/2005/70/index.html.
Повний текст джерелаGratton, Martin Nicholas. "Variation of geomagnetic field intensity over the last 45,000 years in Hawaii using the microwave palaeointensity technique." Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402681.
Повний текст джерелаTulloch, Andrew Malcolm. "A study of recent secular variation of the geomagnetic field as recorded by lavas from Mount Vesuvius and the Canary Islands." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317294.
Повний текст джерелаWardinski, Ingo [Verfasser]. "Core surface flow models from decadal and subdecadal secular variation of the main geomagnetic field / Geoforschungszentrum Potsdam. Vorgelegt von Ingo Wardinski." Potsdam : Geoforschungszentrum, 2005. http://d-nb.info/974254991/34.
Повний текст джерелаSilva, Luís Alexandre. "Ecoulements à la surface du noyau, secousses géomagnétiques et prédictions à court terme du champ magnétique terrestre." Paris, Institut de physique du globe, 2010. http://www.theses.fr/2010GLOB0002.
Повний текст джерелаThis thesis reports on a series of investigations directed towards the dual goal of improving our understanding of what drives the time evolution of the Earth's main magnetic field, and of improving our current ability to predict its short-term behavior. For that we first perform core flow inversions for several epochs and compute first estimates of the flow acceleration by computing differences between successive flows. These first results suggest that the flow generating the Secular Variation (SV) is not stationary. Next, we show how both the core flow and core flow acceleration can be computed simultaneously at any given epoch, if the field and its first and second time derivatives (the SV and the Secular Acceleration (SA)) are known. This allows us to unambiguously show that no stationary flow can account for the observed SA. Based on those results, we consider the possibility of improving on the short-term prediction of the field based on a linear extrapolation currently used by the International Geomagnetic Reference Field (IGRF) by using a method based on a steadily accelerated flow. Then we independently consider the possibility of increasing the spatial resolution of the predictive SV model currently used by IGRF. From all of the above, we conclude that the main limitation to shortterm predictions of the field is the occurrence of sudden changes in the SA (geomagnetic jerks). We thus investigate the type of core ow acceleration changes that are needed to account for those jerks and focus on the 2003 ge
Hartmann, Gelvam Andre. "ARQUEOMAGNETISMO NO BRASIL: VARIAÇÕES DA INTENSIDADE DO CAMPO MAGNÉTICO TERRESTRE NOS ÚLTIMOS CINCO SÉCULOS." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/14/14132/tde-17032011-100832/.
Повний текст джерелаThe Earth\'s magnetic field varies in different timescales, from milliseconds to billions of years. Magnetic data from observatories and satellites indicate that the dipole moment has continuously been decreasing for the past 150 years. This decay is associated to the presence of non-dipole sources covering a wide region that encompasses the South Atlantic and part of South America; in Brazil, the contribution of the non-dipole fields varies strongly with latitude. In the archeomagnetic timescale (~1,000-10,000 years), the evolution of the Earth\'s magnetic field is not well established, mainly due to the scarcity of data from southern hemisphere, which contributes with only 5% of the intensity data for the past 4,000 years. South America is the terra incognita of archeointensity, counting only a handful of results from Peru, Ecuador and Bolivia. This thesis presents the first archeomagnetic results from Brazil. In order to investigate different contributions of non-dipolar sources, we concentrated our sampling in two regions located in different latitudes the Northeast and Southeast regions of Brazil. In the Northeast region, all samples were collected in the city of Salvador (BA), the first Brazilian capital settled in 1549 AD. In the Southeast region, sampling was conducted in the cities of Anchieta (ES), Rio de Janeiro (RJ), Niterói (RJ), Iperó (SP), Piracicaba (SP) and Botucatu (SP). All paleointensity data was obtained from architectural fragments (bricks and some tiles) dated between 1550 AD and 1920 AD. The age of bricks and tiles was established on the basis of archeological studies and the historical record of the buildings, providing age uncertainties of less than 30 years for most of the samples. Paleointensity estimates were obtained by two methods: (a) double-heating with measurements in room temperature, using the modified version of the Thellier protocol; (b) double-heating with measurements in high temperatures, using the Triaxe protocol. After measurements and magnetic corrections, all samples were screened using strict selection criteria resulting in 23 high-quality new site-mean intensity values (from 584 analyzed specimens, with a success rate of 57%). These results were integrated into two curves of geomagnetic intensity variation for each studied region over the past five centuries. These curves reveal an oscillating dipole moment for the past five centuries, a behavior not predicted in currently available geomagnetic field models, thus providing key information on the dipole and non-dipole field evolutions in this timescale. The rapid intensity changes described in these curves permit the application of archeointensity techniques as an archeological dating tool, as exemplified by the dating of a house from the Pelourinho area, in Salvador city.
Venuti, A. "Variability of the climatic antarctic system during the Plio-Pleistocene: Paleomagnetism contribution." Thesis, 2007. http://hdl.handle.net/2122/3803.
Повний текст джерелаINGV
Unpublished
2.2. Laboratorio di paleomagnetismo
reserved
Wardinski, Ingo [Verfasser]. "Core surface flow models from decadal and subdecadal secular variation of the main geomagnetic field / vorgelegt von Ingo Wardinski." 2004. http://d-nb.info/974156817/34.
Повний текст джерелаBatt, Catherine M., M. C. Brown, Sarah-Jane Clelland, M. Korte, P. Linford, and Zoe Outram. "Advances in archaeomagnetic dating in Britain: New data, new approaches and a new calibration curve." 2017. http://hdl.handle.net/10454/16501.
Повний текст джерелаArchaeomagnetic dating offers a valuable chronological tool for archaeological investigations, particularly for dating fired material. The method depends on the establishment of a dated record of secular variation of the Earth's magnetic field and this paper presents new and updated archaeomagnetic directional data from the UK and geomagnetic secular variation curves arising from them. The data are taken from publications from the 1950's to the present day; 422 dated entries derived from existing archaeo and geomagnetic databases are re-evaluated and 487 new directions added, resulting in 909 entries with corresponding dates, the largest collection of dated archaeomagnetic directions from a single country. An approach to improving the largest source of uncertainty, the independent dating, is proposed and applied to the British Iron Age, resulting in 145 directions from currently available databases being updated with revised ages and/or uncertainties, and a large scale reassessment of age assignments prior to inclusion into the Magnetic Moments of the Past and GEOMAGIA50 databases. From the significantly improved dataset a new archaeomagnetic dating curve for the UK is derived through the development of a temporally continuous geomagnetic field model, and is compared with previous UK archaeomagnetic dating curves and global field models. The new model, ARCH-UK.1 allows model predictions for any location in the UK with associated uncertainties. It is shown to improve precision and accuracy in archaeomagnetic dating, and to provide new insight into past geomagnetic field changes.
Arts and Humanities Research Council