Medium Scale Travelling Ionospheric Disturbances (MSTIDs) are quasi-wavelike structures in ionospheric density that can be sensed using Global Navigational Satellite Service (GNSS) Total Electron Content (TEC) techniques and coherent scatter radars such as the Super Dual Auroral Radar Network (SuperDARN). MSTIDs, especially those observed during quiet times and on the night side, have been known to be driven by electrodynamic instability processes, such as the Perkins instability. In this work, SuperDARN is used in conjunction with GNSS TEC data to investigate MSTIDs during a major geomagnetic storm on September 7-8th, 2017. The interval of this study is in the North American region between 23UT and 3UT, during the peak of the storm, when Kp reached 9. MSTIDs during the interval were investigated by previous studies. However, the roles of electrodynamic instability processes and atmospheric gravity waves (AGWs) in driving the MSTIDs were not determined. GNSS TEC fluctuations associated with the MSTIDs were strong, reaching up to half of background TEC. In SuperDARN, MSTID signatures were observed in power measurements. Meanwhile, SuperDARN line-of-sight (LOS) plasma velocity corresponding to MSTID structures exceeded $pm$500 m/s. This systemic change in the polarity of SuperDARN LOS velocities is indicative of strong polarization electric fields and therefore driving electrodynamic instability processes. This work therefore presents signatures of storm time electrified MSTIDs in mid-latitude North America. / Master of Science / The upper atmosphere contains a region called the ionosphere, where ionized gas called plasma exists. This plasma can be sensed using satellites and ground-based receivers. Specifically, Global Navigational Satellite Service constellations, such as GPS, are good candidates for this technique. This method yields a column density measurement of electrons and is known as GNSS TEC. Most of the time, GNSS TEC is used in a low resolution format, but a high-resolution format is available. This high-resolution GNSS TEC allows for smaller structures in the ionosphere to be investigated. Ionospheric plasma can also be sensed using ground based radar systems, such as the Super Dual Auroral Radar Network (SuperDARN). Combining GNSS TEC and SuperDARN allows for investigation of disturbed structures in the Ionosphere. These structures include wave-like behavior, with time scales under 30 minutes, called Medium Scale Travelling Ionospheric Disturbances (MSTIDs). When these MSTIDs are investigated during times where the Sun is especially active, some unexpected results are found. Most importantly, SuperDARN radars see plasma velocity behave as if it is affected by MSTID structures. This suggests that the buoyancy force which drives the MSTIDs is an electric force instead of a pressure gradient. This behavior has been shown before, but only at night times, specifically when the Sun is not as active. Therefore, this work presents a new kind of MSTIDs.

The 2017 Great American Eclipse provided an excellent opportunity for scientists and engineers to study the ionosphere. The dynamics of the ionosphere are affected by the amount of solar radiation it receives and a total solar eclipse produces a short perturbation to the incoming solar radiation. Analyzing how the ionosphere reacts to this type perturbation could lead to new levels of understanding of it. This study develops a nonlinear filter that estimates the state of the ionosphere's 3-D electron density profile given total electron content (TEC) measurements from dual-frequency GPS receivers located on the ground and on low-Earth-orbiting spacecraft. The electron density profile is parameterized by a bi-quintic latitude/longitude spline of Chapman Profile parameters that define the vertical electron density profile. These Chapman parameters and various latitude and longitude partial derivatives are defined at a set of latitude/longitude spline grid points. Bi-quintic interpolation between the points defines the parameters' values and the corresponding Chapman profiles at all latitude/longitude points. The Chapman parameter values and their partial derivatives at the latitude/longitude spline nodes constitute the unknowns that the nonlinear filter estimates. The filter is tested with non-eclipse datasets to determine its reliability. It performs well but does not estimate the biases of the receivers as precisely as desired. Many attempts to improve the filter's bias estimation ability are presented and tried. Eclipse datasets are input to the filter and analyzed. The filter produced results that suggest that the altitude of peak electron density increased significantly near and within the eclipse path and that the vertical TEC (VTEC) was drastically decreased near and within the eclipse path. The changes in VTEC and altitudes of peak electron density caused by the eclipse leave a lasting effect that alters the density profile for anywhere from 15 minutes to several hours. / MS / The 2017 Great American Eclipse garnered much attention in the media and scientific community. Solar eclipses provide unique opportunities to observe the ionosphere’s behavior as a result of irregular solar radiation patterns. Many devices are used to measure this behavior, including GPS receivers. Typically, GPS receivers are used to navigate by extracting and combining carrier phase and pseudorange data from signals of at least four GPS satellites. When the position of a GPS receiver is well-known, information about the portion of the ionosphere that the signal traveled through can be estimated from the GPS signals. This estimation procedure has been done with ground-based and orbiting GPS receivers. However, fusing the two data sources has never been done and will be a primary focus of this study. After demonstrating the performance of the estimation algorithm, it is used to estimate the state of the ionosphere as it was perturbed by the 2017 Great American Eclipse.

Earth's ionosphere is a region of the upper atmosphere that consists of an energetic and electromagnetically reactive plasma. This region plays an important role in over-the-horizon and satellite radio communications, satellite orbits, and can electrically couple into human infrastructure like pipelines and power cables. Activity in the ionosphere is tightly coupled to the near-Earth space plasma region called the magnetosphere. This region is formed by interactions between the energetic particle outflow from the sun called the Solar Wind and Earth's magnetic field. Models of the coupling between these regions typically take a "sun to mud" perspective, as mass and energy from the sun are transferred into the magneto- sphere and ultimately into the upper atmosphere. However, the ionosphere also receives energy directly from ultra-violet radiation from the solar surface. This radiation is the nominal source of ionization in the upper atmosphere, but certain celestial events alter the magnitude of radiation that reaches the upper atmosphere. In the case of a solar eclipse, the moon directly shields a large portion of the Earth from solar radiation. This decreases both the temperature and ionization rate of the upper atmosphere, which in turn decreases the conductivity. A solar flare on the other hand increases the available ionizing energy, and consequently increases the conductivity of the ionosphere. Because the ionosphere is electrically coupled to the magnetosphere, changes in conductivity must necessarily affect the way that coupling occurs. In Chapters 1 and 3, we introduce some of the instrumen- tation used in observing magnetosphere-ionosphere coupling dynamics, as well as some of the difficulties associated with remote instrument operations in the high-latitude regions of Earth. Chapter 4 presents a case study of an Antarctic total solar eclipse, in which magnetic waves are observed from both northern and southern polar regions. The body of work in Chapter 5 suggests that large spatial scale variations in ionospheric conductivity related to solar eclipses are associated with geomagnetic substorms. All together, the research herein highlights the importance of considering ionospheric conductivity as a controlling parameter for magnetosphere-ionosphere coupling. / Doctor of Philosophy / Earth's upper atmosphere consists of an energetic and electromagnetically reactive plasma. This region plays an important role in over-the-horizon and satellite radio communications, and can impact human infrastructure. Activity in this region is influenced by plasma in space near Earth. This region is formed by interactions between energetic particles from the sun and Earth's magnetic field. It is occasionally the case that this near-Earth plasma is disturbed and rapidly moves into the upper atmosphere, resulting in brilliant auroral displays. One of the important factors that controls how this plasma and energy moves is the conductivity of the upper atmosphere region. This varies with latitude and season, but also changes more rapidly during special solar events. In the case of a solar eclipse, the moon directly shields a large portion of the Earth from solar radiation. This decreases both the temperature and ionization rate of the upper atmosphere, which in turn decreases conductivity. A solar flare on the other hand increases conductivity. In Chapters 2 and 3, we introduce some of the instruments used to observe the upper atmosphere plasma regions, as well as some of the difficulties associated with remote instrument operations in the high-latitude regions of Earth. Chapter 4 presents a case study of an Antarctic total solar eclipse, in which magnetic waves are observed from both northern and southern polar regions. Chapter 5 suggests that solar eclipses are associated with the previously mentioned plasma transfers from near-Earth space into the atmosphere. All together, the research herein highlights the importance of considering conductivity as a controlling parameter for energy and plasma transfer in the two regions.

Thesis (Ph. D. (Physics and Electronics))--Rhodes University, 2006.

Made available in DSpace on 2014-06-11T19:30:31Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-09-20Bitstream added on 2014-06-13T18:40:49Z : No. of bitstreams: 1 aguiar_cr_dr_prud.pdf: 7725475 bytes, checksum: 7556eafce637936e645a266c88f16618 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O efeito da ionosfera é a maior fonte de erro sistemático nos sinais transmitidos pelos satélites do GNSS (Sistema Global de Navegação por Satélite), o qual afeta principalmente a acurácia do posicionamento e navegação pelo GNSS quando se utiliza de receptores de simples frequência. Este erro sistemático é diretamente proporcional ao TEC (Conteúdo Total de Elétrons) presente ao longo do caminho percorrido pelo sinal na ionosfera e inversamente proporcional ao quadrado da frequência deste sinal. Devido à natureza dispersiva da ionosfera, o TEC pode ser determinado a partir das observáveis coletadas com receptores GNSS de dupla frequência, possibilitando o monitoramento e a modelagem da ionosfera. Atualmente, os usuários de receptores de simples frequência podem corrigir o erro sistemático devido à ionosfera utilizando modelos como o de Klobuchar, o NeQuick, os GIMs (Mapas Globais da Ionosfera), entre outros. Neste trabalho é apresentado um método para gerar uma Grade Ionosférica (GI) e seu nível de confiança (GIVE), a fim de melhorar a acurácia em aplicações de posicionamento e navegação pelo GNSS, além de fornecer... / The effect of the ionosphere is the largest error source on the L band signals broadcasted by GNSS (Global Navigation Satellite Systems) satellites, which mainly affects the accuracy of GNSS positioning and navigation when a single frequency receiver is used. The systematic error due to the ionosphere is directly proportional to TEC (Total Electron Content) along the signal path and inversely proportional to the square of the transmitting frequency. Due to the ionosphere’s dispersive nature, TEC can be determined with dual frequency GNSS measurements, allowing the modeling and monitoring of the ionosphere. Currently, users of single frequency receivers can correct the systematic error due to the ionosphere using models such as Klobuchar, the NeQuick the GIMs (Global Ionosphere Maps), and others. This work presents a proposed method to generate an Ionospheric Grid (GI) and Grid Ionospheric Vertical Error (GIVE), which can be used to improve the accuracy ... (Complete abstract click electronic access below)

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Science

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International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / The ionosphere is a critical link in the earth's environment for space-based navigation, communications and surveillance systems. Signals sent down by the GPS satellites can provide an excellent means of studying the complex physical and chemical processes that take place there. GPS uses two frequencies to ascertain signal delays passing through the ionosphere. These are measured as errors and used to correct position solutions. Since this process is a means of measuring columns of Total Electron Content (TEC), multiple top-soundings from the GPS constellation could provide significant detail of the ionospheric pattern and possibly lead to enhancement of predictions for selectable areas and sites. This paper addresses transforming the GPS propagation delays (errors) into TEC and providing TEC contours on a PC-style workstation in real and integrated time and discusses a worldwide ionospheric network monitoring system.