Thesis (M.Sc.)--University of Adelaide, Mawson Institute of Antarctic Research, 1970.

xiv, 270 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Mawson Institute for Antarctic Research, University of Adelaide, 1970

Thesis--University of Adelaide. Thesis (Ph. D.)--Mawson Institute for Antarctic Research, University of Adelaide, 1970. / Biblioggraphy: p. 252-270.

Over the years, the study of the aurora has drawn on many different aspects of physics and geophysics in an attempt to explain this common phenomenon. Two prominent magnetic effects which are associated with auroral displays are geomagnetic bays and Pi 2 micropulsations. Both these geomagnetic perturbations attain a maximum amplitude in the auroral zone, but may also be seen in mid and low latitude regions. A bay may be described as the magnetic field of a westward flowing current in the auroral zone coupled with an eastward flowing return current in the mid-latitude and polar cap regions. The means by which Pi 2 micropulsations propagate from the auroral zone centre of activity to mid and low latitude field points is not as yet known. To study the propagation characteristics of Pi 2 micropulsations, a set of five fluxgate magnetometer units was set up stretching across the continent from Victoria, B.C. to Montreal, P.Q. with all stations lying on approximately geomagnetic latitude 56°N. Continuous recordings of H, D and a filtered H component (bandpass 25 - 200 sec.) were made from June 1, 1965 till Aug. 15, 1965. Further information on pertinent disturbances was obtained from stations distributed over the continents of North America and Antarctica. A theoretical study of some of the possible modes of propagation was carried out and specific characteristics of each mode were established in order to permit a check with the experimental data obtained. The pulsations of interest were digitized and power spectra as well as Fourier spectra were computed for the H and D components. The position in longitude of the source of the disturbance was determined making use of pulsation amplitudes, bay amplitudes, and the direction of the disturbance vectors in the horizontal plane. An intensive investigation of the polarization of the pulsations in the horizontal plane was carried out, making use of the complete chain of several cycles but drawing each cycle separately for comparison purposes. This analysis disagrees with previous claims that Pi 2 pulsations are polarized anticlockwise after local midnight and clockwise before local midnight. On the basis of the analysis performed with the data, it was found that the mode of propagation most likely responsible for the transfer of Pi 2 activity from high to mid latitudes could be described by a plane electromagnetic wave propagating approximately normal to the earth's magnetic field lines through the lower E-region of the ionosphere. It is found that the maximum period in a Pi 2 event increases with increasing Kp index in the range Kp ~0 + to 2o. This complements the earlier observation that the dominant period in a Pi 2 event decreases as the Kp index increases; this fact is also verified in the analysis of the experimental data. It is found that the number of peaks in the frequency spectrum of a Pi 2 event increases approximately linearly with increasing Kp . / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (Ph. D.)--University of Washington, 1988. / Vita. Bibliography: leaves [148]-156.

Thesis (Ph.D.)--York University, 2009. Graduate Programme in Earth and Space Science and Engineering. / Typescript. Includes bibliographical references (leaves 149-174). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR51732

Thesis (Ph. D.)--University of Adelaide, 1989. / Includes bibliographical references (leaves 117-130).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 102-108).

Thesis (Ph.D. 1974) from the Dept. of Physics, University of Adelaide.

Investigamos a possibilidade de amplificação de ondas eletromagnéticas no plasma situado nas proximidades dos pólos geomagnéticos a uma altitude de até cerca de cinco raios terrestres. Nesta região ocorre o fenômeno conhecido como "Radiação Quilométrica das Auroras", o qual é uma conseqüência da interação entre o vento solar e a magnetosfera. É feita inicialmente uma ampla revisão das características observacionais conhecidas do fenômeno. Em seguida, é discutido o maser de elétron-cíclotron como possível mecanismo gerador para o fenômeno. Neste sentido, é feita inicialmente uma revisão dos principais trabalhos teóricos, os quais utilizaram o mecanismo de maser na sua formulação de freqüência complexa. Por fim, principia-se um estudo da Radiação Quilométrica das Auroras fazendo uso do maser na formulação de vetor de onda complexo. Os parâmetros físicos necessários para os cálculos de amplificação foram obtidos a partir de um modelo especialmente criado, o qual reproduz de forma aproximada as condições existentes na região aurora!, supondo inclusive um particular gradiente de densidade na direção perpendicular ao campo geomagnético. Os elementos do tensor dielétrico são calculados na aproximação de plasma localmente homogêneo e a função de distribuição considerada consiste na soma de uma maxwelliana de baixa temperatura mais uma cone-de-perda do tipo Dory-Guest-Harris relativística. A relação de dispersão é resolvida exatamente, mantendo-se todos os harmônicos e ordens de raio de Larmor necessários para garantir a convergência da solução. Foram reali zados também cálculos de traçados de raios na aproximação da óptica geométrica através do método de Poeverlein. Constatou-se que quando a razão ent re as freqüências de pla.sma e de cíclotron elet rônicas é Wpe/De < O, 1, as ondas que se propagam no modo ('X t raordinário rápido são amplificadas em freqüências muito próximas à freqüência. de cíclo t ron eletrônica e em ângulos próximos à perpendicular ao campo geomagnético. No caso oposto, Wpe/De > O, 1, são necessários valores cada vez maiores da componente do vetor de onda paralela ao campo magnético para. ocorrer amplificação, a qual é progressivamente menor. Os cálculos ele traçados ele raios mostraram que a escala espacial de variação de parâmetros, perpendicularmente ao campo magnético, é um fator muito importante na amplificação, e que a distância. necessária para uma dada amplificação pode se reduzir substancialmente quando aumenta o gradiente de densidade. / We investigate the possibility of electromagnetic wave amplification in the plasma situated over the geomagnetic peles up to a height around five earth radii. In this region occurs the most intense wave emission phenomenon in the terrestrial magnetosphere, known as "Aurora! Kilometric Radiation", which is a consequence of the solar wind-magnetosphere interaction. Initially, we make a comprehensive review on the known observational characteristics of the phenomenon. Next, the electron-cyclotron maser is discussed as a possible generation mechanism for the phenomenon, anel a review is made on the most important theoretical works, which applied the maser in the complex frequency formulation. We then begin a study on the Auroral Kilometric Radiation applying the maser mechanism in its complex wave frequency formulation . The physical parameters needed for the calculations were obtained from a particular model, especially created to approximately reproduce the real conditions in the aurora! zone, taking into account even a particular density gradient, perpendicular to the geomagnetic field. The components of the dielectric tensor are calculated in the locally homogeneous plasma approximation and the electron distribution function is taken as the sum of a cold maxwellian plus a relativistic Dory-Guest-Harris distribuition. The dispersion relation is exactly solved with all harmonics and powers of Larmor radius needed for the convergency of the solutions. We have also clone ray-tracing studies in the geometrical opti cs approximation, using the Poeverlein's method. We have found Ll1at , wh en Lhe electronic plasma to cyclotron frequencies ratio is Wpe/De < 0.1, the waves t hat propagatc in the fast extraordinary mode are amplified at frequencies very near to Lhe c.\·c lot ron frequency anel in the quasi-perpendi cular direction of the geomagnetic field. On t.hc olhcr hand , c.v·PE/De > 0.1 , the component of the wave vector parallel to the magnet i c fi eld musL have larger values for the amplification to occur, progressively smaller in valu e. The ray-L racing st udies have shown that the spatial scale of the inhomogeneity, perp endi cular to the magnetic field , is a very important factor in the amplification, anel that the cli stance to obtain a given amplification can be substantially reduced when the clensity gra.client is increasecl.