Yes / There 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.

Geomagnetic excursions, brief deviations in geomagnetic field behaviour from that expected during 'normal' secular variation, remain some of the most enigmatic features of geomagnetic field behaviour. This thesis presents high-resolution records of geomagnetic excursions recorded at the Blake-Bahama Outer Ridge in the Western North Atlantic. The highest resolution record yet of the Blake geomagnetic excursion (~125 ka) is measured in three cores from Ocean Drilling Program Site 1062 (ODP Leg 172). These cores have sufficiently high sedimentation rates (>10 cm ka^-1) to allow detailed reconstruction of the field behaviour at these sites during the excursions. Previous reconstructions of geomagnetic field behaviour during excursions from marine cores have been limited by low-resolution age models. This thesis discusses a new approach, whereby measurements of excess ²³⁰Th (²³⁰Th_xs) are used to constrain relative variations in sedimentation rate. Modifications are suggested to the methods previously used to calculate the concentration of ²³⁰Th_xs and a new MATLAB® program is developed and described that allows rapid and flexible calculation of ²³⁰Th_xs. Using this new approach, the duration (6.5±1.3 kyr) and age (129-122 ka) of the Blake excursion are accurately constrained. A palaeomagnetic study is also conducted on two ODP Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge to obtain a high-resolution record of the Laschamp geomagnetic excursion (~41 ka). The Blake excursion is found to be of 'long' duration (6.5±1.3 kyr) whilst the Laschamp excursion is relatively short (<400 years) showing that excursions do not have a characteristic duration, linked to the conductivity of the inner core, but instead occupy a continuous range of durations. The records of both the Blake excursion and the Laschamp excursion from the Blake-Bahama Ridge sites also show rapid transitions to excursional geomagnetic pole positions (less than 500 years), much faster than often quoted for full geomagnetic reversals. Based on current estimates for reversal durations, this would imply that excursions and reversals are controlled by different processes.

No description available.

A magnetohydrodynamic (MHD) cavity-resonance model is developed to study the ultra low frequency (ULF) response in the magnetosphere to an external compressional impulse. It is assumed that the magnitude of the impulse is small enough such that non-linear terms remain negligible. The MHD differential equations are derived in a cold, non-uniform plasma imbedded in a cylindrical ambient field geometry and are solved using numerical finite difference integration methods. The crucial feature of the model is that it allows for the investigation of the response within the magnetospheric cavity to an impulse that has both temporal and spatial form. There is strong observational evidence that low-latitude Pi 2 pulsations have, or are associated with, a global propagation mechanism. Evidence alluding to the global nature of low-latitude Pi 2 is the characteristically low azimuthal (or axial) wavenumbers, (Irnl ;S 1 ). Further evidence of the global nature of Pi 2 is the lack of arrival time difference between globally separate events, as well as the similarity in the spectral content of globally separate events. As an application, the cavity-resonance model is applied to investigate the Pi 2 pulsation event. The cavity-resonance waves are excited by an impulsive perturbation at the magnetopause which is centred about the midnight meridian. The excitation signal is chosen representing the causal Pi 2 mechanism thought to be associated with the sudden, short circuiting of the cross-tail current to the auroral oval. Various aspects of the cavity-resonance wave modes are investigated and the appropriateness of this type of modelling for -the study of Pi 2 is evaluated. Numerical integration and well as Fourier and Laplace methods are used to investigate the transmission of the impulsive signal through the magnetosphere. Coupling between the isotropic (cavity) and the transverse Alfven (resonance) mode is studied. The effect of the plasmapause is considered. Longitudinal variations of polarization as well as the latitudinal phase variations of the perturbed fields are computed. Computational results are compared with observational features of the Pi 2 event. / Thesis (Ph.D.)-University of Natal, Durban, 1993.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22257号 / 理博第4571号 / 新制||理||1656(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田口 聡, 教授 秋友 和典, 准教授 藤 浩明 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

No description available.

The first comprehensive study of equatorial- to mid-latitude ionospheric electric fields (plasma drifts) is presented, using extensive incoherent scatter radar measurements from Jicamarca, Arecibo, and Millstone Hill, and F-region ion drift meter data from the polar orbiting DE-2 satellite. Seasonal and solar cycle dependent empirical quiet-time electric field models from equatorial to mid latitudes are developed, which improve and extend existing climatological models. The signatures of electric field perturbations during geomagnetically disturbed periods, associated with changes in the high-latitude currents and the characteristics of storm-time dynamo electric fields driven by enhanced energy deposition into the high-latitude ionosphere, are studied. Analytical empirical models that describe these perturbation drifts are presented. The study provided conclusive evidence for the two basic components of ionospheric disturbance electric fields. It is shown that magnetospheric dynamo electric fields can penetrate with significant amplitudes into the equatorial- to mid-latitude ionosphere, but only for periods up to 1 hour, consistent with results from the Rice Convection Model. The storm-time wind-driven electric fields are proportional to the high-latitude energy input, vary with local time and latitude, and have largest magnitudes during nighttime. These perturbations affect differently the zonal and meridional electric field components. It is shown that equatorial zonal electric fields (vertical drifts) can be disturbed up to 30 hours after large enhancements in the high-latitude currents. These perturbation electric fields are associated with enhanced high-latitude energy deposition taking place predominantly between about 1-12 hours earlier and found to be in good agreement with the Blanc-Richmond disturbance dynamo model. A second class of perturbations occurs around midnight and in the dawn-noon sector with delays of about 18-30 hours between the equatorial- and the high-latitude disturbances , and maximizes during locally quiet geomagnetic times. The latitudinal variation of the meridional disturbance electric fields (zonal drifts) is also presented. It is shown that these perturbation electric fields are predominantly downward/equatorward at all latitudes and due to both prompt penetration and disturbance dynamo electric fields. These results are also generally consistent with predictions from global convection and disturbance dynamo models.

The objective of this dissertation is the development of computer simulation-based models for the modeling of upper ionosphere, starting from the first principles. The models were validated by exact analytical benchmarks and are seen to be consistent with experimentally obtained results. This area of research has significant implications in the area of global communication. In addition, these models would lead to a better understanding of the physical processes taking place in the upper ionosphere.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24422号 / 理博第4921号 / 新制||理||1703(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 齊藤 昭則, 教授 石岡 圭一, 教授 田口 聡 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

No description available.