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.

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.

No description available.

This thesis presents the studies of aurora using three observation instruments; the SAPPHIRE SOUTH VHF radar system, the ASC (All-Sky Camera) system at Rabbit Lake, Saskatchewan, and the 50-MHz CW (Continuous Wave) bistatic Doppler radars in the 1981 campaign. The SAPPHIRE SOUTH radar system, which has a high temporal and frequency resolution, is a multi-beam CW bistatic VHF Doppler radar system. Two transmitters, located at La Crete (Alberta), and Gillam (Manitoba), transmitted on four transmitter beams for each transmitter and intersected with four receiver beams from Saskatoon, Saskatchewan to form 32 radar target regions in the lower E-region of the ionosphere. The ASC system at Rabbit Lake provides digitized high resolution optical auroral images at several wavelengths (557.7 nm, 630.0 nm) and for the whole visible spectrum. The observing region of the ASC system covered all the radar target regions of the SAPPHIRE SOUTH radar system. The 50 MHz CW bistatic Doppler radars in the 1981 campaign had a special radar setup with three transmitters and two receivers to provide multiple radar beams with different aspect and flow angles. The AE index and Kp index data have been compared with the radar Doppler spectral characteristics extracted by using software designed for peak-finding and curve-fitting. The radar data received by the SAPPHIRE SOUTH radar system have been compared with the optical data obtained by the ASC: system in Rabbit Lake. The results showed that strong Type 1 and Type 3 radar auroral echoes were received along the auroral arc alignment while weak Type 2 echoes were observed in the direction perpendicular to the auroral arc alignment. The power of radar auroral echoes received along the auroral arc alignment was well correlated with the standard deviation of the optical auroral emission inside the radar target region. The non-linear theory of the Type 3 radar auroral echoes has also been examined. A fading analysis has been applied to the SAPPHIRE SOUTH radar data to examine whether the electromagnetic ion cyclotron (EMIC) wave caused the fading of VHF radar auroral signals. The results showed that fading frequency ranges of Type 3 and Type 4 echoes were consistent with electric field oscillation and primary particle modulation arising from EMIC waves. The results of statistical studies on the data obtained from the radars in the 1981 campaign showed that the power of radar auroral backscatter echoes received by the radar link with a large aspect angle (4.08°) and a small assumed flow angle (6.17°) correlated well with the AE index. Regardless of the AE index, strong radar auroral backscatter echoes were observed by the radar link with smallest aspect angle (1.57°). Type 1 and Type 5 radar auroral backscatter mostly occurred for large values of the AE index, while Type 2 and Type 3 radar auroral backscatter echoes were mostly observed for small values of the AE index.

Observations have been made at Sanae (gm. lat. -63,71°) on occurring auroral forms, (diffuse and pulsating aurora), and simultaneous occurring VLF phenomena, (whistlers and auroral hiss) . Two studies are presented in this thesis. (a) A comparison of the positions of auroral forms and the positions of field lines, along which whistlers propagate, is made and it is found that: (i) Diffuse aurora occurs on closed field lines and indirect evidence shows that this is also the case for pulsating aurora. (ii) For two periods of data the separation of diffuse aurora from the plasmapause ranges from < 0,9 L to < 0,2 L but during a third period, the diffuse aurora lies, at least partially, within the plasmasphere. (b) An investigation into the association between pulsating aurora and pulsating auroral hiss is made and it is shown that: (i) A common identical pulsation period of 0,75 s and high coherency exists between the light intensity of an auroral patch and the intensity of the associated pulsating auroral hiss. This suggests a wave-particle interaction as a common modulation mechanism. (ii) Cyclotron instability (gyroresonance) or Cerenkov radiation mechanisms occurring in the equatorial plane do not account for the time delays, typically between 0,90 s and 0,157 s, found to be present between, the two phenomena, where the incident auroral electrons, responsible for the auroral patch light intensity, are observed to arrive before the auroral hiss emissions. The results of the analysis in (a) are reported in The Journal of Atmospheric and Terrestrial Physics, 39, 1429, 1977. / Thesis (Ph.D.)-University of Natal, 1978.

[11] 212 leaves : ill., plates ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1974) from the Dept. of Physics, University of Adelaide

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (p. 168-204).

This thesis describes the application of tilting-filter photometry to the study of the airglow and aurora. Previous South African photometric research is reviewed. Optical instrumentation and techniques used in airglow and auroral research are reviewed. The transmission characteristics of narrowband interference filters are discussed. The analogue meridian-scanning tilting-filter photometry system used at Sanae, Antarctica is described. Shortcomings of this system have been identified, and modifications have been made to improve its spatial and temporal resolution. Details are given of the computer-controlled digital photometry system which replaced the analogue system. Equations are derived for the conversion of raw photometric data (analogue chart deflections or digital photon counts) to absolute emission intensities. The accuracy of the intensities obtained depends on the absolute calibration of the photometer, the transmission characteristics of the filter used to isolate the spectral feature of interest, and the effects of atmospheric extinction and scattering. The influence of these factors on observed emission intensities is discussed. Various models used to determine atmospheric correction factors are reviewed. It is shown that atmospheric correction factors can have a significant effect on both emission intensities and intensity ratios. The procedure used to determine the transmission characteristics of interference filters is described, as is the procedure used to cross-calibrate secondary light sources. The transmission characteristics of the filters and the brightnesses of the light sources were both found to have changed appreciably with age. The observation of a magnetospheric substorm at Sanae (L ≃ 4) is used to illustrate the use of a meridian-scanning tilting-filter photometer system in auroral research. The ratio I(557.7)/ I(391.4) observed at Sanae was found to be lower than expected, as were the OJ airglow emission intensities. A prototype digital photometer system was used aboard a ship, to observe the airglow in the region of the South Atlantic Anomaly. Significant N₂⁺ lNG emissions at 391.4 nm were measured, confirming the presence of discernable particle precipitation in the region. The 0I557.7 and 630.0 nm intensities measured from the ship were found to be lower than expected. This, combined with low airglow and auroral intensities measured at Sanae, is a cause for concern. It is recommended that further checks be made regarding the brightness of the calibration sources.

Terrestrial auroras are visible-light events caused by charged particles trapped by the Earth's magnetic eld precipitating into the atmosphere along magnetic eld lines near the poles. Auroral events are very dynamic, changing rapidly in time and across large spatial scales. Better knowledge of the low of energy during an aurora will improve understanding of the heating processes in the atmosphere during geomagnetic and solar storms. The Auroral Spatial Structures Probe is a sounding rocket campaign to observe the middle-atmosphere plasma and electromagnetic environment during an auroral event with multipoint simultaneous measurements for fine temporal and spatial resolution. The auroral event in question occurred on January 28, 2015, with liftoff the rocket at 10:41:01 UTC. The goal of this thesis is to produce clear observations of the magnetic eld that may be used to model the current systems of the auroral event. To achieve this, the attitude of ASSP's 7 independent payloads must be estimated, and a new attitude determination method is attempted. The new solution uses nonlinear least-squares parameter estimation with a rigid-body dynamics simulation to determine attitude with an estimated accuracy of a few degrees. Observed magnetic eld perturbations found using the new attitude solution are presented, where structures of the perturbations are consistent with previous observations and electromagnetic theory.

Bibliography: leaves 117-130 / xii, 130 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1989