Dissertations / Theses on the topic 'Geomagnetic variation'
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Bloxham, J. "Geomagnetic secular variation." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372644.
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Heller, Rainer. "The paleomagnetic field's long-term mean intensity and secular variation /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6840.
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Pressling, Nicola Justine. "Pacific geomagnetic secular variation : the story from Hawaii." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441187.
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Lean, Candida Mary Bevan. "Geomagnetic palaeosecular variation recorded in North and Central American speleothems." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240751.
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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.
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Knowledge of the intensity of the Earth's magnetic field throughout geological time can deliver a wealth of information regarding the development of the planet. The nature of the geomagnetic field is dependent on processes that occur deep in the Earth's core. By analysing long period changes in geomagnetic field intensity inferences can be made about conditions in the Earth's interior far back into Earth history. The microwave palaeointensity technique is a relatively recent addition to palaeomagnetic investigation. High-frequency microwaves, which are resonant with the constituent magnetic system of a rock, are used to isolate and progressively remove the magnetisation of samples acquired at the time of formation in a controlled manner. By exciting the magnetic system directly, thermal-type experiments can be conducted, whilst minimising the risk of chemical alteration, which is a major cause of experimental failure.
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Finlay, Christopher Charles. "Hydromagnetic waves in Earth's core and their influence on geomagnetic secular variation." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.418244.
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Mitsutake, Gen. "Natural variation in geomagnetic pulsations and preschool children's sleep disturbance and motor activity levels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62799.pdf.
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Allington, M. L., Catherine M. Batt, M. J. Hill, A. Nilsson, A. J. Biggin, and N. Card. "Obtaining archaeointensity data from British Neolithic pottery: A feasibility study." Elsevier, 2021. http://hdl.handle.net/10454/18426.
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YesThere is a significant lack of geomagnetic field strength (archaeointensity) measurements for many archaeological time periods in the United Kingdom (UK). This not only makes past geomagnetic secular variation difficult to model but also limits the development of archaeointensity dating. This paper presents the first archaeointensity study on UK Neolithic material. In this study, twenty-five sherds of Neolithic Grooved Ware pottery from the Ness of Brodgar, Orkney, UK, some with direct radiocarbon dates, were subjected to a full archaeomagnetic investigation with the aim of increasing the amount of archaeointensity data for the UK. Both thermal Thellier and microwave palaeointensity experiments were used to determine which technique would be most suitable for British Neolithic pottery. Three successful archaeointensity results between 35 and 40μT were obtained using thermal Thellier method, which is consistent with the limited data available within a 15° radius and geomagnetic field model predictions from the same time. We separated the results into four different types with an intention of explaining the behaviours that determine the likelihood of achieving an acceptable archaeointensity estimate. The feasibility of obtaining geomagnetic field strength information during the UK Neolithic from ceramics has been demonstrated and the results provide a solid basis for improving our knowledge of geomagnetic secular variation during archaeological time in Britain.
The Andy Jagger Fund, University of Bradford, for supporting the stay at the University of Liverpool and Crafoord Grant, Sweden, No. 20160763. The radiocarbon dates were funded by AHRC NF/2017/2/7.
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Wardinski, 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.
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Wardinski, 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.
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Onovughe, Elvis. "Geomagnetic diurnal variation studies using global models & observatory data at quiet & moderately disturbed times." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2032947/.
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In this thesis we investigate and analyse the nature and behaviour of the external field variations of the geomagnetic field for quiet and moderately disturbed days using geomagnetic observatory measurements and field models. We use spherical harmonic modelling, led by available geomagnetic observatory measurements and past models (particularly the Comprehensive Model of Sabaka et al. 2004). As an initial step, we extended the lifespan of the Comprehensive Model (CM4) beyond its 2002.5 lifespan to allow for use of current data. We produced profile plots of the diurnal field and generated global maps of the field and compare these with the CM4 model, to see how well the CM4 model could reasonably predict ground variation of the diurnal field outside its lifespan and for days away from quiet time. The comparison shows that away from quiet time period, the CM4 model is producing more reasonable predictions than expected, despite the lack of active data in the original model dataset. The CM4 model fits the regional type features of the geomagnetic components, but not doing well predicting the short term features during period of rapid variations (seen as ‘wiggles’ in the profile plots) , especially for the X- component. Also, comparing the modelled diurnal maps of the CM4 and observatory data shows that increasing the spherical harmonic degree produces a better match between the CM4 model and the data. Our result reveals that the external field description included in the CM4 model could not sufficiently explain the field variation for days away from quiet time. The CM4 model predicts the Y- and Z- components variations better than the X; this may be due to the fact that the X component is more affected by external field sources. As a result we introduced the use of an additional geomagnetic activity index (the RC index), to enable us to establish the nature of the rapid variation seen in the data for days away from quiet time. We looked for this using eigenanalysis (covariance matrices, eigenvectors and eigenvalues), detrending the data sequences with spline fits, and comparing the observatory data residuals with the RC index values. We also looked at the coherence and correlation between small scale features showing up in the rapid variation, to try to establish the global scale of the variations. We analysed this by simple running average method, correlation and cross-correlation coefficients between the residuals of the observatory data components and the RC index. Our results show that our data for days away from quiet time, particularly the X component, include a strong component in the rapid variations related to large-scale external field variation arising from the magnetospheric ring current. For example we are able to reproduce features in our plots that show a very strong coherence and correlation existing between the X component of our observatory data residuals and the RC index. This is also seen in the same components of the observatories at different locations within the same geographical region, and at some different geographical regions. This allows us to characterise the RC index as being a good representation for rapid variations globally. Also, it makes us optimistic that it may be useful to look at rapid variation observatory results for combined observatory stations as a good technique for remote referencing in aeromagnetic surveying.
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Gratton, 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.
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Biggin, Andrew J. "An experimental and analytical assessment of geomagnetic intensity variation since the Devonian : links with global geological processes." Thesis, Kingston University, 2001. http://eprints.kingston.ac.uk/20670/.
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This study was broadly concerned with acquiring geomagnetic palaeointensity estimates and interpreting existing data in the wider context of the global geodynamic system. Two-hundred and ninety-eight samples from nine suites of Mesozoic and Permian intrusions (comprising thirty-one individual rock units) from eastern Australia were subjected to rock magnetic and palaeodirectional analyses. The grain size distributions of these were generally observed to contain a significant fraction of large pseudo-single domain (PSD) and multi-domain (MD) grains. This frequently allowed a substantial part of their blocking temperature spectrum (- 350°C) to be overprinted by a thermal event affecting this region during the mid-Cretaceous. The modified Thellier palaeointensity method was employed on samples from seven of the intrusion suites producing virtual dipole moment (VDM) estimates generally lower than the present value (8 x 1022 Am2) and variable in quality. Mean values of VDM were obtained for the following periods: 90 Ma « 5.9 x 1022 Am2); 127 Ma (7.9 x 1022 Am2); 172 Ma (1.2 x 1022 Arn); 200 - 178 Ma (6.3 x 1022 Am2); 255 Ma (7.5 x 1022 Arrr'). Despite being in good agreement with previously acquired data, few of these estimates satisfied all conventional acceptance criteria and consequently a reliability (R) factor was invoked to allow qualitative comparisons of estima~es tobe made. A simulated Thellier experiment was also performed on pre-treated rock samples containing magnetic grains dominantly within the single domain (SD) range. This produced a surprising amount of variable non-ideal behaviour. In particular, a number of samples significantly overestimated the 'palaeointensity' when only a low temperature, seemingly ideal, portion of their blocking temperature spectra was used. Five proposed mechanisms of non-ideal behaviour succeeded in explaining most of this non-ideal behaviour and correcting the results of 50% of the samples. One of these, 'demagnetisation bias,' could be developed into an extremely useful tool for correcting convex-down NRM-TRM plots produced by assemblages of Ml) grains and allow this widespread problem to be overcome in future palaeointensity studies. The global dipole moment record for the period 400 - 10 Ma was subject to a detailed statistical analysis allowing it to be segmented into periods defined by the distribution of the data themselves. Additionally, a system of grouping estimates into 'rock suites' was developed to avoid over-representation of secular variation (SV) in the record. Variation of poloidal field strength (PFS; recorded in VDM estimates) since the Devonian was shown to be largely decoupled from geomagnetic reversal frequency except during superchrons when its lower limit may have been raised. It was discovered that periods of intense true polar wander (TPW) and large igneous province (LIP) emplacement, which have previously been associated with changes in reversal, frequency, may perturb the geodynamo's capacity to generate poloidal field but certainly do not control it An excellent time correlation between PFS and the supercontinent amalgamation-dispersion cycle since the Devonian was observed. The following model, comprising four' phases, was developed to explain this. (l) Prior to the formation of Pangaea (> 350 Ma) the 'upper and lower mantle convected separately, the latter was hot allowing only a small heat flux across the CMB, and consequently PFS was kept low. (2) During the final assembly of Pangaea (350 - 325 Ma), there was a catastrophic avalanche of cold material through the 660 km transition into the lower mantle which increased CMB heat flux and PFS dramatically. (3) The maintenance of Pangaea through the period 325 - 180 Ma allowed both the upper and lower mantle to wann gradually, causing PFS to fall steadily. (4) In the mid-Jurassic, the continents began to disperse and the high temperature contrast between lithosphere and mantle provided the subducting slabs with sufficient momentum to penetrate the 660 km transition and gradually cool the lower mantle, PFS has risen (steadily or in small jumps) since this time as a consequence. This model is entirely consistent with long-term trends in PFS since the Devonian, and provides a benchmark to be tested by the addition of more palaeointensity data and quantitative mantle modelling.
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Chapana, Randi Synnøve Hegdal. "The Relative Influence of Solar Radiative and Solar Geomagnetic Variation on the Dynamics of the Polar Upper Mesosphere." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18887.
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Resent research indicates that there might be a connection between perturbation of the Earth's geomagnetic field caused by solar wind, and the atmospheric circulation. In this project the mesospheric meridional and zonal wind, obtained from the SuperDARN radars Goose Bay, Hankasalmi, Kapuskasing, King Salmon, Kodiak, Pykkvibær, Saskatoon and Stokkseyri in the northern hemisphere was compared with the global Ap index along with the measure for solar radiance, the F10.7 index. Wind data from the SuperDARN radars were available for every hour and geomagnetic and irradiance data for every month. The solar atmospheric tides along with seasonal effects were removed from the wind data and the perturbation of the residual wind due to Ap and F10.7 was used to see if any connection between the mesospheric wind and Ap/F10.7 could be found, and if they influenced the wind in a similar manner. A tendency for more equatorwards and eastwards winds during periods of high geomagnetic activity was found. In addition, this effect was observed to increase with increasing geomagnetic latitude for the zonal wind. Ap and F10.7 often affected the wind in a similar manner, making it hard to distinguish the two. Using linear regression, the correlation between them was found to be high over the timescales of this study.
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Tulloch, 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.
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Gough, H. "The latitudinal variation of geomagnetic pulsation amplitude and phase : A model of the magnetosphere and a study of two selected intervals." Thesis, University of York, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354381.
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Clelland, Sarah-Jane. "Developing archaeomagnetic dating in the British Iron Age." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5448.
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Archaeomagnetism is an area of research that utilises the magnetic properties of archaeological materials to date past human activity. This research aimed to use the evidence of past geomagnetism, as recorded by archaeological and geological materials, to identify and characterise short timescale changes in the Earth¿s magnetic field. This contribution to the discipline focused on the first millennium BC, as there is evidence that during this time the Earth¿s magnetic field experienced rapid changes in direction. This work focused on an established weakness in archaeomagnetic studies, i.e. the application of archaeological information to assign a date range to the magnetic directions. The date ranges for 232 magnetic directions from 98 Iron Age sites were reviewed and a programme of fieldwork produced 25 new magnetic directions from 11 Iron Age sites across Britain. The approach developed in this thesis has made significant improvements to the data examined, which represent the prehistoric section of the British secular variation curve (SVC). These data have been incorporated into the British archaeomagnetic dataset that now comprises over 1000 magnetic directions and will be used to generate future British SVCs. The potential of the near continuous records of geomagnetic secular variation from British lake sediment sequences to SVCs was explored. This showed that these sediments have recorded the relative changes in the Earth¿s magnetic field but the dating and method of constructing the British master curve requires revision. As SVCs are predominately used as calibration curves for archaeomagnetic dating, this work provides a foundation for a revised and extended British SVC. This revision would be to the mutual benefit of studies in archaeology and archaeomagnetism, as the latter could potentially enable highresolution dating of Iron Age material, providing a viable alternative to radiocarbon dating.
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Wardinski, 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.
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Silva, 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.
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Dans ce mémoire nous présentons une série d'études dont le double objectif est de mieux comprendre les phénomènes qui gouvernent l'évolution du champ magnétique principal de la Terre, et d'améliorer notre capacité actuelle à en prédire l'évolution à court terme. Pour cela, nous réalisons d'abord quelques inversions de la Variation Séculaire (VS) pour plusieurs époques et calculons une première estimation de l'accélération de l'écoulement à partir d'écoulements successifs. Ces calculs suggèrent que les écoulements qui génèrent la VS ne sont pas stationnaires. Nous montrons ensuite comment calculer simultanément ces écoulements et leur accélération pour une époque donnée, si le champ ainsi que sa première et seconde dérivées temporelles (la VS et l'accélération séculaire(AS)) sont connues. Ceci nous permet de montrer sans ambiguïté qu'un écoulement stationnaire ne peut pas rendre compte de la AS observée. Nous considérons ensuite la possibilité d'améliorer la prévision à court terme du champ, actuellement basée sur une extrapolation linéaire, dans le cadre du modèle "International Geomagnetic Reference Field" (IGRF), en utilisant une méthode basée sur un écoulement uniformément accélérée. Nous considérons aussi la possibilité d'augmenter la résolution spatiale de la VS prédictive actuellement utilisée par l'IGRF. De ces études, nous concluons que le principal obstacle à la prédiction à court terme du champ vient des changements brusques de la AS (jerks). Nous étudions la nature des changements d'accélération rendant compte du `jerk' de 2003. Nous montrons que ce changement n'est hélas pas compatible avec un mécanisme simple tel que les oscillations de torsionThis 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
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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/.
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O campo magnético da Terra varia em diferentes escalas de tempo, de milissegundos a bilhões de anos. Os dados de observatórios magnéticos e satélites obtidos nos últimos 150 anos indicam que o momento do dipolo magnético terrestre está diminuindo continuamente. Essa queda está associada à presença de fontes não-dipolares do campo em uma extensa região que abrange todo o Atlântico Sul e uma porção da América do Sul, sendo que no Brasil a contribuição dessas fontes varia fortemente com a latitude. Em escala de tempo arqueomagnética (~1.000-10.000 anos) a evolução do campo magnético terrestre não é tão bem estabelecida, principalmente em função da escassez de dados no hemisfério Sul, que contribui com apenas 5% dos dados de intensidade obtidos para os últimos 4.000 anos. A América do Sul, com alguns poucos resultados no Peru, Equador e Bolívia, pode ser considerada a terra incógnita da arqueointensidade. Nesta tese são apresentados os primeiros resultados arqueomagnéticos para o território brasileiro. Foram escolhidas duas regiões de estudo, o Nordeste e o Sudeste do Brasil, situadas em diferentes faixas de latitude de modo a investigar diferentes contribuições de componentes não-dipolares do campo. No Nordeste, as amostras foram coletadas na cidade de Salvador (BA), a primeira capital do Brasil, fundada em 1549 AD. Na região Sudeste a amostragem foi efetuada nas cidades de Anchieta (ES), Rio de Janeiro (RJ), Niterói (RJ), Iperó (SP), Piracicaba (SP) e Botucatu (SP). Nas duas regiões, a paleointensidade do campo magnético terrestre foi obtida em materiais construtivos (tijolos e alguns fragmentos de telhas) datados entre 1550 AD e 1920 AD. As idades desses materiais foram estabelecidas com base em estudos arqueológicos e registros históricos das construções, fornecendo incertezas inferiores a 30 anos para a grande maioria das amostras. As paleointensidades foram estimadas utilizando-se dois métodos: (a) duplo aquecimento com medidas em temperatura ambiente, pelo protocolo de Thellier modificado por Coe; (b) duplo aquecimento com medidas contínuas em alta temperatura, pelo protocolo Triaxe. Após as medidas e correções magnéticas, todas as amostras foram analisadas com base em rigorosos critérios de seleção, que resultaram em 23 novas determinações de intensidade de alta qualidade (correspondendo a um total de 584 espécimes analisados, com uma taxa de sucesso de 57%). A partir desses resultados foram traçadas duas curvas de variação da intensidade do campo magnético para cada uma das regiões estudadas, abrangendo os últimos 500 anos. Essas curvas revelam uma oscilação do momento de dipolo nos últimos cinco séculos, que não foi prevista nos modelos de campo disponíveis atualmente, trazendo implicações importantes no entendimento da evolução dos campos dipolar e não-dipolar nessa escala de tempo. As variações rápidas descritas nessas curvas permitem aplicar o arqueomagnetismo como ferramenta de datação arqueológica, como exemplificado pela datação de uma casa do Pelourinho em Salvador.The 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.
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Davidson, Nigel Charles. "The analysis of geomagnetic storm-time variations." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/13577.
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The earth is bathed in an ever changing magnetic environment due to fluctuations in the solar wind. The external field induces currents within the earth which cause a secondary internal field. The ratio of internal to external parts of the magnetic potential is known as the response and may be derived from measurements of the field at the surface. The response of the earth is dependent on the spatial form of the field and distribution of conductivity within the earth. The analysis of numerous geomagnetic storms, large disturbances in the field surrounding the whole earth, is presented with the aim of determining a reliable response function which enables an estimate to be made of the average conductivity of the upper mantle. The compilation of a database of geomagnetic storms was a major part of the work. All the suitable storm events were selected between 1957 and 1982 to give 44 storms. The entire set of hourly values were checked for errors and corrections made where necessary. Where data were missing their values were interpolated using information from nearby observatories. The lower the frequency of external magnetic variations the deeper the penetration into the earth. The frequency content of geomagnetic storms allows depths approaching 1500km to be investigated. The observations of magnetic field were Fourier transformed and attention focussed on the Fourier coefficients of the lowest frequencies, 0.03 to 1 cycle per day. From Spherical Harmonic Analysis in the frequency domain it was found that a pure P1o spherical harmonic model is acceptable for the spatial form of the field at the frequencies of most interest. Thus the source is assumed to be a simple ring current in common with most of the previous research. The Fourier coefficients of the X and Z magnetic components were then fitted to the appropriate P1o model which allows the separate internal and external parts to be evaluated. A robust method, to reduce the influence of anomalous values, was used for determining the optimum fit to the Fourier coefficients. The technique was assessed by examining the distribution of residuals.
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Mann, R. J. "Aspects of the day-to-day variability of Sq." Thesis, University of Exeter, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370932.
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Soyer, Wolfgang. "Analysis of geomagnetic variations in the Central and Southern Andes." [S.l.] : [s.n.], 2002. http://www.diss.fu-berlin.de/2002/134/index.html.
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McMillan, David G. "Statistical analyses of geomagnetic dipole variations, reversals and geodynamo simulations /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3090447.
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Okubo, Ayako. "Studies on geomagnetic spatial and temporal variations in volcanic area." 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/145088.
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Kyoto University (京都大学)0048
新制・課程博士
博士(理学)
甲第11320号
理博第2878号
新制||理||1430(附属図書館)
22963
UT51-2005-D71
京都大学大学院理学研究科地球惑星科学専攻
(主査)教授 田中 良和, 教授 大志万 直人, 教授 鍵山 恒臣
学位規則第4条第1項該当
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Smith, Graeme. "Late glacial palaeomagnetic secular variations from France." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/11404.
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Openshaw, Steven J. "Palaeosecular variation observed in speleotherms from western China and northern Spain." Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307629.
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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.
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This thesis comprises two parts. The main part is involved with laboratory studies of the palaeosecular variation of the geomagnetic field as recorded in lake sediments. The natural remanent magnetization of the sediments cored from the two Italian maar lakes, Lago di Monticchio and Lago di Martignano, has been studied. Further studies were carried out on the sediments of Lago di Martignano to determine the cause of large variations in the magnetic intensity of the sediments with an age of 6000 years BP and it was concluded that this was caused by the arrival of Neolithic man and the advent of agriculture in the catchment area. The directional record for this lake was also compared to the established record for north west Europe. Several declination and inclination features could be correlated between the two records. The record from Lago di Martignano can be accepted as a regional palaeomagnetic reference curve for central Italy. Cores up to 50m long were taken from Lago di Monticchio. Whilst not yet firmly dated, it is agreed that this record spans the last 250,000 years. A relative palaeointensity record has been calculated and spectral analysis has been carried out. It is concluded provisionally that the palaeointensity recorded in the sediments was effected by the astronomical frequencies associated with precession of the earth, the eccentricity and the obliquity of the Earth's orbit. The second part of this thesis is concerned with modelling the palaeosecular variations as recorded in sediments around the world through the Holocene, i.e. the last 10,000 years. The properties of sequential secular variation records from sediments are compared with palaeosecular variation scatter determined from sets of lava flows. It is concluded that a comparison between PSV recorded in lava flows and lake sediments is valid.
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Nakano, 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.
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Nam, Young-sun. "GPS determination of diurnal and semidiurnal variations in earth rotation parameters and the geocenter /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Saturnino, 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.
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A description of the temporal variations of the main geomagnetic field (i. E. , the secular variation, or SV) is crucial to the understanding of core dynamo generation. It is known with high accuracy at observatory locations, which are globally unevenly located, hampering the determination of a global pattern of these variations. Satellites have allowed global surveys of the field and its SV. Their data has been used by global spherical harmonic models using data selection criteria to reduce external contributions. SV small spatial scales may not be well described by these models, and can show significant errors compared to ground measurements. This study attempts to extract temporal variation time series from satellite measurements as it is done at observatory locations. We follow a Virtual Observatories (VO) approach, defining a global mesh of VOs at satellite altitude. We apply an Equivalent Source Dipole (ESD) technique. For each VO and a given time interval all measurements are reduced to a unique location, leading to time series similar to those available at the ground. Synthetic data is first used to validate the approach. We then apply our scheme to Swarm mission measurements. We locally compare the VO-ESD derived time series to ground observations and to satellite-based model predictions. The approach is able to describe field's time variations at local scales. The global mesh of VO time series is used to derive global spherical harmonic models. For a simple parametrization the model well describes the trend of the magnetic field both at satellite altitude and at the surface. Nevertheless more complex modelling can be made to properly profit of VO-ESD time seriesLa 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
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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.
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Parmi les méthodes de reconstitution de l'histoire du champ géomagnétique, l'étude des variations de la production atmosphérique d'isotopes cosmogéniques s'est récemment développé. Cette production est modulée au premier ordre et aux échelles multimillénaires par l'intensité du champ géomagnétique. Son enregistrement dans les archives de l'environnement terrestre en apporte une lecture indépendante, donc complémentaire des méthodes paléomagnétiques. Ce travail vise à retracer les changements de taux de production de 10Be enregistrés dans les sédiments marins, afin de restituer les variations du moment géomagnétique depuis environ 800 000 ans. Les rapports 10Be/9Be authigéniques mesurés par Spectrométrie de Masse par Accélérateur le long de trois séquences de différentes latitudes, permettent de caractériser la production globale de 10Be sur deux intervalles de temps. (1) Lors de la baisse du moment dipolaire associée à l'excursion Laschamp (~41 000 ans BP), la surproduction de 10Be à 38°N et 2°S, confirmée par des mesures de 10Be/230Thxs, est identique à celle restituée dans les glaces du Groenland. (2) L'étude menée sur une carotte prélevée à l'équateur couvrant l'intervalle 800 000 – 250 000 ans BP (époque Brunhes), révèle les phases successives de surproduction globale de 10Be déclenchées par les chutes de moment dipolaires liées à l'inversion Brunhes-Matuyama d'une part et d'autre part à une dizaine d'excursions documentées. La calibration de ces enregistrements avec des valeurs absolues disponibles dans la littérature permet la quantification des moments dipolairesAmong 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
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Labbé, François. "Ondes hydro-magnétiques dans un modèle Quasi-géostrophique du noyau terrestre." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAU033/document.
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Les variations du champ magnétique terrestre sont documentées par les observatoires au sol et les satellites en orbite basse, pour des échelles de temps de l'année au siècle.Sur ces périodes, la dynamique du noyau externe -- là où est principalement généré le champ magnétique -- est fortement influencée par la rotation terrestre, qui tend à imposer une invariance dans la direction parallèle à l'axe de rotation.Dans cette thèse, j'étudie un modèle s'appuyant sur cette hypothèse de bidimensionnalité du champ de vitesse, le modèle quasi-géostrophique.Je présente une nouvelle dérivation de ce modèle par une approche variationnelle, plus adaptée aux fortes pentes des frontières du domaine sphérique.Je présente une étude modale des ondes hydro-magnétiques, qui pour la première fois prend en compte l'impact d'un champ magnétique imposé non-zonal.Deux groupes d'ondes magnéto-hydrodynamiques apparaissent alors : les ondes magnéto-Coriolis (centennales) et les ondes d'Alfvéen de torsion (interannuelle).Je décris l'évolution des ondes à mesure que l'on intensifie l'effet de la rotation, jusqu'à atteindre des paramètres géophysiques.Je discute également dans quel mesure une version du modèle quasi-géostrophique où la force de Lorentz est représentée par des produits quadratiques du champ magnétique est adapté pour l'interprétation de calculs numériques tridimensionnels de la dynamo. J'observe que pour les paramètres aujourd'hui accessibles à ces calculs, les forces magnétiques sont faibles. À long terme, nous espérons utiliser le modèle quasi-géostrophique dans le contexte de l'assimilation de données satellitairesVariations of the Earth's magnetic field are documented by ground observatories and low-orbiting satellites, for time scales from year to century.On such periods, dynamics of the outer core -- where the creation of the magnetic field takes place -- is strongly influenced by the Earth rotation, which tends to impose invariance of the flow in the direction parallel to the rotation axis.In this thesis report, I study a model based on this bi-dimensional velocity field hypothesis, the quasi-geostrophic model.I present a new mathematical formulation of this model through a variational approach, better suited to steep slopes on the boundaries of the spherical domain.I present a modal study of hydromagnetic waves, taking into account for the first time the impact of a non-zonal imposed magnetic field.Two groups of hydromagnetic waves are present : centennial magneto-Coriolis waves and interannual torsional Alfvén waves.I describe evolution of those waves as the effect of rotation is intensified until Earth-like parameters are reached.I also discuss in what measure an other version of the quasi-geostrophic model, where Lorentz force is represented by quadratic products of the magnetic field, can be adapted to understand tridimensional dynamo numerical simulations.I observe that for parameters available today, magnetic forces are weak.In the future, we hope to use the Quasi-geostrophic model in the context of satellite data assimilation
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Clelland, Sarah-Jane, and Catherine M. Batt. "Geomagnetic secular variation as recorded in British lake sediments and its application to archaeomagnetic studies." 2012. http://hdl.handle.net/10454/5934.
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Lake sediments can play an important role in understanding and reconstructing temporal characteristics of the geomagnetic field, as they potentially offer near continuous high-resolution archives of magnetic information extending throughout the Holocene. To date lake sediment geomagnetic data has typically been excluded from British archaeomagnetic secular variation curves (SVC) due to uncertainties with the acquisition of magnetisation by lake sediments. This paper presents the argument that, with regards to British datasets, the real problem lies with poor chronological control and sets out to illustrate that with British archaeomagnetic data some progress has been made. The results indicate that it is not currently possible to resolve secular variation on a time scale of ¿100 years from published British lake sediment data but more success has been made with data from archaeological sediments. This level of detail has been considered necessary for the incorporation of lake sediment data into the British archaeomagnetic dataset, as the ability to resolve short-term geomagnetic changes is critical for the integration of any dataset into the British SVC. As the latter is predominantly employed to date archaeological architecture and artefacts requires that it has the ability to resolve changes over timescales relevant to human lifetimes. Using currently available data this retrospective critique confirms that, in archaeological sediments, depositional and thermoremanent magnetisation can record the same direction over the same time interval.
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Nahayo, Emmanuel. "An investigation in the use of satellite data to develop a geomagnetic secular variation model over Southern Africa." Thesis, 2011. http://hdl.handle.net/10413/5379.
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Time variations of the geomagnetic field can be classified into two main categories
of internal and external origin with respect to the surface of the Earth. It has been
found that the variations that take place on longer time scales (~ 1 year and longer)
are commonly known as secular variation (SV) and are of internal origin. There is a
need to develop SV models using satellite data as the use of ground data is not always
possible with many limitations including the limited data points and lack of data over
ocean areas that are not easily accessible. Two regional geomagnetic field modelling
techniques namely polynomial surface modelling (PolyM) and Spherical Cap Harmonic
Analysis (SCHA) were applied to CHAMP satellite data recorded between 2001 and
2005 to investigate the use of satellite data to develop a geomagnetic SV model over
southern Africa. The restricted area of investigation is between 10° and 40° South in
latitude and between 10° and 40° East in longitude. The resulting regional models of
this investigation were validated against the two widely used global field models IGRF
10 and CHAOS using the available ground survey data obtained during the same period
over southern Africa. The results suggest that the regional field models can be derived
based entirely on satellite data. However, the regional SV models can be improved by
combining both high quality satellite and ground survey data, since they lack the high
quality of a global field model like CHAOS.Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.
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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.
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Batt, 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.
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yesArchaeomagnetic 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
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Chen, Kuo-Hang, and 陳國航. "High-resolution geomagnetic secular variation record around Taiwan for the past 2,000 years: A case study of marine core MD05-2907 in southern Okinawa Trough." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/78853235291802244259.
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Soyer, Wolfgang [Verfasser]. "Analysis of geomagnetic variations in the Central and Southern Andes / Wolfgang Soyer." 2002. http://d-nb.info/964989336/34.
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Venuti, A. "Variability of the climatic antarctic system during the Plio-Pleistocene: Paleomagnetism contribution." Thesis, 2007. http://hdl.handle.net/2122/3803.
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In the framework of a gradual global warming, which is one of the topic of major interest in the recent years and which importance is resumed in the Intergovernmental Panel on Climate Change (IPCC), it is important the study of the variability of the Earth’s system at the high latitudes i.e., in Artic and Antarctic areas, because these are the regions more sensitive to climatic changes. The possibility to study marine sedimentary sequences from Antarctica thus represented an important opportunity to investigate such climatic variability. Cold water mass formation in the Southern Ocean is involved in the global thermohaline circulation (THC) through the convection and inter-ocean exchanges of surface, intermediate and bottom waters. This work focus on the study of marine sequences cores from mid-high latitudes from strategic locations far and near the continental margin of Antarctica: (1) ANTA 95-157 (62°05.95'S) and ANTA 96-16 (66°20.09'S) cores are a long transect from New Zealand and Ross Sea slightly south of the present day Polar Front and the Pacific Antarctic Ridge, respectively; (2) MD97-2114 (42°22.32'S) core is on the northern side of Chatham Rise, east of New Zealand; (3) ODP Site 1166 (67°41.77'S) and 1167 (66°24.01'S) are in Prydz Bay continental shelf and slope, respectively. It has been provided a detailed magnetostratigraphy of the sequences and have been investigated magnetic proxies, which reflect variations in mineralogy, grain-size, and concentration of the magnetic fraction. Environmental magnetic data, along with the chronology derived by the magnetostratigraphy, provided an important contribution to our understanding of environmental and climate changes during the time intervals here examined. The cores ANTA and MD97-2114 span the shift from predominant 41-ka to predominant 100-ka glaciation cycles at around 1.0–0.9 Ma, (the Mid-Pleistocene Climate Transition (MPT)) that was centered at 922±12 ka and lasted about 40±9 ka. The amplitude of the 100-ka cycle abruptly increased much later on, at 641±9 ka. The transition was accompanied by an increase in 18O and decrease in 13C but the causes may be many and further information about changes in global ice volume during this period needed. In this core it has been found evidence of orbital influence on sedimentary processes.
The core MD97-2114 records long-term variation of the upper Circumpolar Deep Water component of the Deep Western Boundary Current and manifests a stepwise modification of the THC during the transition. ODP Site 1166 and 1167 provide a record of the process involved in the story of the glacial expansion and retreat of the ice at the margin of the continent in Prydz Bay during the Plio-Pleistocene. Preliminary results from SEDANO cores shows downcore variations in concentration, mineralogy, and grain-size of magnetic minerals. In particular, there is a relative increase of moderate coercivity respect to low-coercivity minerals (magnetite) during glacials and a millennial scale variability of the magnetic grain size characterizes the last glacial (core SED 12 and 13) and it may be related to changes in the bottom current velocity.INGV
Unpublished
2.2. Laboratorio di paleomagnetismo
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