Dissertations / Theses on the topic 'Ionospheric waves'
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1
Borderick, James David. "Ionospheric signatures of ultra low frequency waves." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/9170.
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Ultra Low Frequency (ULF) waves have been studied for many years and the observation and modelling of such phenomena reveals important information about the solar-terrestrial interaction. Being ubiquitous in the collisionless terrestrial space plasma environment, ULF waves represent important physical processes in the transfer of energy and momentum. This thesis comprises three distinct studies to observe, model and analyse ULF phenomena. The first two studies focus on ULF wave observations at high-latitudes in the terrestrial ionosphere using a collection of both space- and ground-based instruments. The first study provides a detailed analysis of the time evolution of a ULF wave using the characteristics of the observed ULF wave as input-parameters to a 1-D numerical model. As the wave signature evolves towards a Field Line Resonance (FLR) a change in the incident wave mode from a partially Alfvénic wave to a purely shear Alfvénic wave is observed. The second study presents statistics of 25 large spatial-scale ULF waves with observations from a high-latitude Doppler sounder and ground-based magnetometers, complemented by model results. The third and final study describes the implementation of a well established radar technique ("double-pulse"), which is new for the Super Dual Auroral Radar Network (SuperDARN), which aims to provide an unprecedented temporal resolution for ULF wave studies. The new pulse sequence increases the temporal resolution of SuperDARN by a factor of three. Preliminary findings suggest this technique yields impressive results for ionospheric scatter with steady phase values but that the method cannot be used for data when the phase is rapidly changing or if the data originates from slowly decorrelating plasma irregularities. The running of two independent pulse sequences on the stereo channels of the Hankasalmi radar has also enabled, for the first time, the observation of cross-contamination between the radar channels.
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Norton, Andrew David. "Analysis of Ionospheric Data Sets to Identify Periodic Signatures Matching Atmospheric Planetary Waves." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101791.
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Atmospheric planetary waves play a role in introducing variability to the low-latitude ionosphere. To better understand this coupling, this study investigates times when oscillations seen in both atmospheric planetary waves and ionospheric data-sets have similar periodicity. The planetary wave data-set used are temperature observations made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). These highlight periods during which 2-Day westward propagating wave-number 3 waves are evident in the mesosphere and lower thermosphere. The ionospheric data-set is Total Electron Content (TEC), which is used to identify periods during which the ionosphere appears to respond to the planetary waves. Data from KP and F10.7 indices are used to determine events that may be of external origin. A 17-year time-span from 2002 to 2018 is used for this analysis so that both times of solar minimum and maximum can be studied. To extract the periods of this collection of data a Morlet Wavelet analysis is used, along with thresholding to indicate events when similar periods are seen in each data-set. Trends are then determined, which can lead to verification of previous assumptions and new discoveries.Master of Science
The thermosphere and ionosphere are impacted by many sources. The sun and the magnetosphere externally impact this system. Planetary waves, which originate in the lower atmosphere, internally impact this system. This interaction leads to periodic signatures in the ionosphere that reflect periodic signatures seen in the lower atmosphere, the sun and the magnetosphere. This study identifies these times of similar oscillations in the neutral atmosphere, the ionosphere, and the sun, in order to characterize these interactions. Events are cataloged through wavelet analysis and thresholding techniques. Using a time-span of 17 years, trends are identified using histograms and percentages. From these trends, the characteristics of this coupling can be concluded. This study is meant to confirm the theory and provide new insights that will hopefully lead to further investigation through modeling. The goal of this study is to gain a better understanding of the role that planetary waves have on the interaction of the atmosphere and the ionosphere.
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Thomas, Edwin Christopher. "Phase and amplitude variations in the wave fields of ionospherically reflected radio waves." Thesis, University of Leicester, 1986. http://hdl.handle.net/2381/35807.
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The wavefronts of high frequency (HF) radio waves received after reflection from the ionosphere exhibit both spatial non-linearities and temporal variations which limit the performance of large aperture receiving arrays. The objective of this investigation was to measure the phase and amplitude of ionospherically propagated signals in order to relate these parameters to the reflection process. This thesis describes the design and construction of a large aperture multi-element array and its implementation for wavefrot investigations. The hardware and software developed to control the equipment and to record the measurements are described. The procedures required to verify the performance of the experimental system are discussed and results are presented which demonstrate the accuracy of the measurements. The array was utilised for studies of signals received from several transmitters situated throughout Western Europe. The results obtained demonstrate the widely different behaviour of signals received over the various propagation paths and these have been related to the modal content of the received signals. Limited periods existed during which a single ionospheric mode was received and data corresponding to this condition have been compared with those which would be expected if the signal consisted of both a specular component and a cone of diffracted rays. This model is unable to explain the experimental results. Numerical models of the received signal were therefore developed. Results of these and comparisons with experimental results suggest that the measured parameters can be explained by the existence of a specular component with a varying direction of arrival (DOA), plus some contribution from random components. The experimental results indicate that the random or diffracted components normally contribute less than 10% of the received power in a single moded signal.
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Takiguchi, Yu. "Emission of whistler waves from an ionospheric tether." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54621.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 121-122).
In this thesis, we analyze how electromagnetic waves propagate in ionosphere around the earth which is magnetized plasma. We calculate the electromagnetic wave field made by a dipole antenna at an arbitrary observation point far from the antenna using the Stationary Phase Method. With this wave field, wave energy flux is calculated, and by integrating this wave energy flux on the sphere around the antenna, the radiation resistance of this antenna is computed. We compare the results with some past analytical and experimental works. We also analyze the wave propagation characteristics. The wave propagation ways are different for different wave frequencies. We precisely analyze this different wave propagation ways by analyzing the group velocity and k surface of the wave. There are intense radiation directions. We discuss the nature of these intense radiation directions and compare the characteristics with the past works. There are spatial oscillations of wave fields and wave energy flux. We also discuss the reason of this oscillation and compare with the past works.
by Yu Takiguchi.
S.M.
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Löfås, Henrik. "Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121898.
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Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced. A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region.
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Frissell, Nathaniel A. "Ionospheric Disturbances: Midlatitude Pi2 Magnetospheric ULF Pulsations and Medium Scale Traveling Ionospheric Disturbances." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/74976.
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The ionosphere is an electrically charged atmospheric region which is coupled to the sun, the magnetosphere, and the neutral atmosphere. The ionospheric state can significantly impact technological systems, especially those which utilize radio frequency energy. By studying ionospheric disturbances, it is possible to gain a deeper understanding of not only the ionosphere itself, but also the natural and technological systems it is coupled to. This dissertation research utilizes high frequency (HF) radio remote sensing techniques to study three distinct types of ionospheric disturbances. First, ground magnetometers and a new mid latitude SuperDARN HF radar at Blackstone, Virginia are used to observe magnetospheric Pi2 ultra low frequency (ULF) pulsations in the vicinity of the plasmapause. Prior to these pulsations, two Earthward moving fast plasma flows were detected by spacecraft in the magnetotail. Signatures of inner magnetospheric compression observed by the Blackstone radar provide conclusive evidence that the plasma flow bursts directly generated the ground Pi2 signature via a compressional wave. This mechanism had previously been hypothesized, but never confirmed. Next, ten SuperDARN radars in the North American Sector are used to investigate the sources and characteristics of atmospheric gravity waves (AGW) associated medium scale traveling ionospheric disturbances (MSTIDs) at both midlatitudes and high latitudes. Consistent with prior studies, the climatological MSTID population in both latitudinal regions was found to peak in the fall and winter and have a dominant equatorward propagation direction. Prior studies suggested these MSTIDs were caused by mechanisms associated with auroral and space weather activity; however, it is shown here that the AE and Sym-H indices are poorly correlated with MSTID observations. A new, multi-week timescale of MSTID activity is reported. This leads to the finding that MSTID occurrence is highly correlated with an index representative of polar vortex activity, possibly controlled by a filtering mechanism that is a function of stratospheric neutral wind direction. Finally, a case study of a radio blackout of transionospheric HF communications caused by an X2.9 class solar flare is presented. This study demonstrates the potential of a novel technique employing signals of opportunity and automated receiving networks voluntarily created by an international community of amateur radio operators.Ph. D.
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Kalkavage, Jean Hogan. "Nonlinear wave-wave interactions in ionospheric plasmas caused by injected VLF and HF waves." Thesis, Boston University, 2014. https://hdl.handle.net/2144/21184.
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Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.The study of wave-wave interactions in the ionosphere is important for designing communication systems, satellite systems, and spacecraft. Ionospheric research also informs laser and magnetic fusion plasma physics. This thesis focuses on two nonlinear wave-wave interactions in the ionosphere. The first interaction is a nonlinear mode conversion. Very Low Frequency (VLF) waves transmitted from the ground travel through the ionosphere as injected whistler waves. The whistler waves interact with naturally-occurring density fluctuations in the ionosphere and are mode converted into lower hybrid waves. The lower hybrid waves accelerate electrons along the geomagnetic field and the resulting beam mode Langmuir waves are detectable by radar. This type of mode conversion may combine additively with a four wave interaction with the same VLF wave as its source. Data collected at the Arecibo Observatory in Puerto Rico during the occurrence of spread F and sporadic E was analyzed. Plasma line enhancements may indicate the nonlinear mode conversion both separately from and in conjunction with the four wave interaction. The second nonlinear wave-wave interaction is the parametric decay instability (PDI) excited by High Frequency (HF) heater waves at the High Frequency Active Auroral Research Program facility in Gakona, Alaska. Resonant PDI cascades downwards, resulting in up-shifted ion line enhancements as detected by radar. This process has been detected in the presence of down-shifted ion line enhancements which may be caused by beating between PDI-produced Langmuir waves, or by naturally occurring ionospheric currents.
2031-01-01
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Negale, Michael. "Investigating the Climatology of Mesospheric and Thermospheric Gravity Waves at High Northern Latitudes." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/6937.
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An important property of the Earth's atmosphere is its ability to support wave motions, and indeed, waves exist throughout the Earth's atmosphere at all times and all locations. What is the importance of these waves? Imagine standing on the beach as water waves come crashing into you. In this case, the waves transport energy and momentum to you, knocking you off balance. Similarly, waves in the atmosphere crash, known as breaking, but what do they crash into? They crash into the atmosphere knocking the atmosphere off balance in terms of the winds and temperatures. Although the Earth's atmosphere is full of waves, they cannot be observed directly; however, their effects on the atmosphere can be observed. Waves can be detected in the winds and temperatures, as mentioned above, but also in pressure and density. In this dissertation, three different studies of waves, known as gravity waves, were performed at three different locations.
For these studies, we investigate the size of the waves and in which direction they move. Using specialized cameras, gravity waves were observed in the middle atmosphere (50-70 miles up) over Alaska (for three winter times) and Norway (for one winter time). A third study investigated gravity waves at a much higher altitude (70 miles on up) using radar data from Alaska (for three years). These studies have provided important new information on these waves and how they move through the atmosphere. This in turn helps to understand in which direction these waves are crashing into the atmosphere and therefore, which direction the energy and momentum are going. Studies such as these help to better forecast weather and climate.
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Yang, Heng 1985. "On the detection of ionospheric waves, relationship with earthquakes and tsunamis." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667175.
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The research of this thesis addresses the detection and characterization of ionospheric waves and its application to traveling ionospheric disturbances (TIDs) induced by the natural events, such as earthquakes and tsunamis. The characterization is done from regional detrended Vertical Total Electron Content (VTEC) maps which are obtained from a set of Global Navigation Satellite System (GNSS) satellites. Note that from the mathematical and signal-processing point of view, the problem presents two key difficulties that are (a) the fact that ionospheric sampling is nonuniform, with different density of samples that somehow reflect the distribution of stations over the earth surface, and (b), that the estimation method can not introduce any constraints in the number of disturbances and their propagation parameters.
In the first contribution of the thesis, we propose a method for detecting the number of simultaneous TIDs from a time series of high-pass-filtered VTEC maps and their parameters. The method, which we refer to as the Atomic Decomposition Detector of TIDs (ADDTID), is tested on the detrended VTEC map corresponding to a simulated realistic scenario from the dense GNSS network, Global Positioning System Earth Observation Network (GEONET) in Japan. The contribution consists of the detection of the exact number of independent TIDs from a nonuniform sampling of the ionospheric pierce points. The solution to the problem is set as the estimation of the representative perturbations from a dictionary of atoms that span a linear space of possible TIDs by means of a variation of the LASSO algorithm. These atoms consist of plane waves characterized by a wavelength, direction, and phase on a surface defined, the part of the ionosphere sounded by the GNSS observation.
As the second contribution, we apply ADDTID on actual VTEC data to the GEONET network. We have studied the Medium Scale TIDs (MSTIDs) during the Spring Equinox day of 21 March 2011. The geophysical contribution is: (a) detection of circular MSTID waves compatible by time and center with a specific earthquake; (b) simultaneous superposition of two distinct MSTIDs, with almost the same azimuth; and (c) the presence of nighttime MSTIDs with velocities in the range 400-600 m/s.
In the third contribution we provide a detailed characterization of the TIDs originated from the total solar eclipse of 21 August 2017, the shadow of which crossed the United States from the Pacific to the Atlantic ocean. This can be modeled in part as if the umbra and penumbra were moving cylinders that intersects with variable elevation angle a curved surface. The result of this is reflected in the time evolution of the TID wavelengths produced by the eclipse, which depend on the vertical angle of the sun with the surface of the earth, and also a double bow wave phenomenon, where the bow waves are generated in advance to the umbra. Finally, we detected a clear pattern of MSTIDs, which appeared in advance of the penumbra, which we could hypothesize as soliton waves associated with the bow wave.
In the fourth contribution we characterized the MSTIDs generated during the Japan Tohoku earthquake of 11 March 2011. We found: (a) a confirmation of the performance of the algorithm in face of simultaneous multi-TID, the robustness to the curvature of the wave fronts of the perturbations and the accuracy of the estimated parameters. The results were double checked by the additional visual inspection from VTEC maps and keogram plots; (b) The detection of different wave fronts between the west and east MSTIDs around the epicenter, consistent in time and space with the post-earthquake tsunami; (c) The complete evolution of the circular MSTIDs driven by the tsunami during the GNSS observable area; (d) The detection of the fast and short circular TIDs related to the acoustic waves of earthquake.Esta tesis aborda la detección y caracterización de las ondas ionosféricas y su aplicación a las perturbaciones ionosféricas itinerantes (TID traveling ionospheric disturbances) inducidas por eventos naturales. La caracterización se realiza a partir de mapas regionales de Contenido Total Vertical de Electrones (VTEC) que se obtienen a partir de medidas de un conjunto de satélites del Sistema Navegación GNSS (Global Navigation Satellite System). Obsérvese que, desde el punto de vista matemático y de procesamiento de señales, el problema presenta dos dificultades: a) el hecho de que el muestreo ionosférico no es uniforme, con una densidad de muestras diferente que refleja de alguna manera la distribución de las estaciones sobre la superficie terrestre, y b) el hecho de que el método de estimación no puede introducir ninguna limitación en el número de perturbaciones y sus parámetros de propagación a detectar. En la primera contribución de la tesis, proponemos un método para detectar el número de TIDs simultáneas de una serie temporal de mapas VTEC filtrados por paso alto y sus parámetros. El método, al que denominamos como el Detector de Descomposición Atómica de TIDs (ADDTID), lo probamos con mapas VTEC, que corresponden a un escenario realista simulado en la red GEONET en Japón. La contribución consiste en la detección del número exacto de TIDs independientes a partir de un muestreo no uniforme de los IPPs de la ionosférica. La solución al problema se establece como la estimación de las perturbaciones representativas a partir de un diccionario de átomos que abarcan un espacio lineal de posibles TIDs mediante una variación del algoritmo LASSO. Estos átomos consisten en ondas planas caracterizadas por una longitud de onda, dirección y fase en una superficie definida. Como segunda contribución, aplicamos ADDTID a los datos VTEC a la red GEONET. Para probar el método, hemos estudiado los MSTIDs durante el día del Equinoccio de Primavera del 21 de marzo de 2011. La contribución geofísica es: (a) la detección de ondas circulares MSTID compatibles por tiempo y centro con un terremoto específico; (b) la superposición simultánea de dos MSTID distintos, con casi el mismo acimut; y (c) la presencia durante la noche de MSTID con velocidades en el rango de 400-600 m/s. En la tercera contribución presentamos una caracterización detallada de los TIDs originados por el eclipse solar total del 21 de agosto de 2017, cuya sombra atravesó los Estados Unidos desde el Pacífico hasta el Océano Atlántico. La evolución temporal de las TID producidas por el eclipse, que dependen del ángulo vertical del sol con la superficie de la tierra, y también aparece en un fenómeno de doble onda de choque. Finalmente, detectamos un patrón claro de MSTIDs, que aparecieron antes de la llegada de la penumbra, lo que podríamos hipotetizar como ondas de solitón asociadas con la onda de choque. En la cuarta contribución caracterizamos los MSTIDs generados durante el terremoto de Tohoku en Japón el 11 de marzo de 2011. Lo encontramos: a) una confirmación de la prestación del algoritmo frente al multi-TID simultáneas, la robustez frente a la curvatura de los frentes de onda de las perturbaciones y la precisión en la estimación de los parámetros. Los resultados se verificaron por duplicado mediante la inspección visual adicional de los mapas de VTEC y de los diagramas de keogramas; b) la detección de diferentes frentes de onda entre los MSTID del oeste y del este en torno al epicentro, coherentes en el tiempo y en el espacio con el maremoto posterior al terremoto; c) la evolución completa de las MSTID circulares que impulsó el maremoto durante el período observable en la zona de observación de los GNSS; y d) la detección de las MSTID circulares cortas y rápidas en el espacio en relación con las ondas acústicas asociadas con el terremoto.
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Hoffmann, Peter, and Christoph Jacobi. "Analysis of planetary waves seen in ionospheric total electron content (TEC) perturbations." Universität Leipzig, 2006. https://ul.qucosa.de/id/qucosa%3A15490.
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Am DLR Neustrelitz wird kontinuierlich die totale Ionosation der Atmosphäre bestimmt und globale Karten der vertikal integrierten Elektronendichte erstellt. Es werden dazu die Signale der Navigationssatelliten-Systeme GPS und GLONASS verwendet. In dieser
Arbeit wird die Verteilung des totalen Elektronengehalt (TEC) oberhalb der mittleren Breiten während der Übergangssaison September bis November 2004 auf langperiodische Variationen im Bereich von mehreren Tagen sowie zonalen Wellenzahlen bis zu 5 untersucht. Die Ergebnisse werden mit einer Analyse von planetaren Wellen aus assimilierten Stratosphärendaten, Radardaten für Temperatur vom Collm Observatorium (51.3◦N, 13.0◦O) und Beobachtungen der kritischen Plasmafrequenz der F2-Schicht (f0F2) mit der Ionosonde in Juliusruh (54.6◦N, 13.4◦O) verglichen, um den meteorologischen Einfluss auf die Variation der Ionosphäre zu studieren.The DLR Neustrelitz regularly produces maps of the total total electron content (TEC) on a global scale using the navigation satellite systems GPS and GLONASS to forecast space weather. In this study we turn our attention to the higher middle latitudes TEC variations during September to November 2004 in a long-period range of several days with a zonal wavenumber up to 5. The results are compared with a planetary wave analysis using assimilated stratospheric data, mesosphere/lower thermosphere radar temperature data at Collm observatory (51.3◦N, 13.0◦E) and the ionosonde observed critical plasma frequency of the F2-layer (f0F2) at Juliusruh (54.6◦N, 13.4◦E) to investigate the meteorological influences on ionospheric variability.
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Hoffmann, Peter, and Christoph Jacobi. "Analysis of planetary waves seen in ionospheric total electron content (TEC) perturbations." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-221930.
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Am DLR Neustrelitz wird kontinuierlich die totale Ionosation der Atmosphäre bestimmt und globale Karten der vertikal integrierten Elektronendichte erstellt. Es werden dazu die Signale der Navigationssatelliten-Systeme GPS und GLONASS verwendet. In dieser Arbeit wird die Verteilung des totalen Elektronengehalt (TEC) oberhalb der mittleren Breiten während der Übergangssaison September bis November 2004 auf langperiodische Variationen im Bereich von mehreren Tagen sowie zonalen Wellenzahlen bis zu 5 untersucht. Die Ergebnisse werden mit einer Analyse von planetaren Wellen aus assimilierten Stratosphärendaten, Radardaten für Temperatur vom Collm Observatorium (51.3◦N, 13.0◦O) und Beobachtungen der kritischen Plasmafrequenz der F2-Schicht (f0F2) mit der Ionosonde in Juliusruh (54.6◦N, 13.4◦O) verglichen, um den meteorologischen Einfluss auf die Variation der Ionosphäre zu studierenThe DLR Neustrelitz regularly produces maps of the total total electron content (TEC) on a global scale using the navigation satellite systems GPS and GLONASS to forecast space weather. In this study we turn our attention to the higher middle latitudes TEC variations during September to November 2004 in a long-period range of several days with a zonal wavenumber up to 5. The results are compared with a planetary wave analysis using assimilated stratospheric data, mesosphere/lower thermosphere radar temperature data at Collm observatory (51.3◦N, 13.0◦E) and the ionosonde observed critical plasma frequency of the F2-layer (f0F2) at Juliusruh (54.6◦N, 13.4◦E) to investigate the meteorological influences on ionospheric variability
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Tshisaphungo, Mpho. "Validation of high frequency propagation prediction models over Africa." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.
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The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.
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Russell, Alexander J. B. "Coupling of the solar wind, magnetosphere and ionosphere by MHD waves." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/2571.
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The solar wind, magnetosphere and ionosphere are coupled by magnetohydrodynamic waves, and this gives rise to new and often unexpected behaviours that cannot be produced by a single, isolated part of the system. This thesis examines two broad instances of coupling: field-line resonance (FLR) which couples fast and Alfvén waves, and magnetosphere-ionosphere (MI-) coupling via Alfvén waves. The first part of this thesis investigates field-line resonance for equilibria that vary in two dimensions perpendicular to the background magnetic field. This research confirms that our intuitive understanding of FLR from 1D is a good guide to events in 2D, and places 2D FLR onto a firm mathematical basis by systematic solution of the governing equations. It also reveals the new concept of ‘imprinting’ of spatial forms: spatial variations of the resonant Alfvén wave correlate strongly with the spatial form of the fast wave that drives the resonance. MI-coupling gives rise to ionosphere-magnetosphere (IM-) waves, and we have made a detailed analysis of these waves for a 1D sheet E-region. IM-waves are characterised by two quantities: a speed v_{IM} and an angular frequency ω_{IM} , for which we have obtained analytic expressions. For an ideal magnetosphere, IM-waves are advective and move in the direction of the electric field with speed v_{IM}. The advection speed is a non-linear expression that decreases with height-integrated E-region plasma-density, hence, wavepackets steepen on their trailing edge, rapidly accessing small length-scales through wavebreaking. Inclusion of electron inertial effects in the magnetosphere introduces dispersion to IM-waves. In the strongly inertial limit (wavelength λ << λ_{e} , where λ_{e} is the electron inertial length at the base of the magnetosphere), the group velocity of linear waves goes to zero, and the waves oscillate at ω_{IM} which is an upper limit on the angular frequency of IM-waves for any wavelength. Estimates of v_{IM} show that this speed can be a significant fraction (perhaps half) of the E_{⊥} × B_{0} drift in the E-region, producing speeds of up to several hundred metres per second. The upper limit on angular frequency, ωIM , is estimated to give periods from a few hundredths of a second to several minutes. IM-waves are damped by recombination and background ionisation, giving an e-folding decay time that can vary from tens of seconds to tens of minutes. We have also investigated the dynamics and steady-states that occur when the magnetosphere-ionosphere system is driven by large-scale Alfvénic field-aligned currents. Steady-states are dominated by two approximate solutions: an ‘upper’ solution that is valid in places where the E-region is a near perfect conductor, and a ‘lower’ solution that is valid where E-region depletion makes recombination negligible. These analytic solutions are extremely useful tools and the global steady-state can be constructed by matching these solutions across suitable boundary-layers. Furthermore, the upper solution reveals that E-region density cavities form and widen (with associated broadening of the magnetospheric downward current channel) if the downward current density exceeds the maximum current density that can be supplied by background E-region ionisation. We also supply expressions for the minimum E-region plasma-density and shortest length-scale in the steady-state. IM-waves and steady-states are extremely powerful tools for interpreting MI-dynamics. When an E-region density cavity widens through coupling to an ideal, single-fluid MHD magnetosphere, it does so by forming a discontinuity that steps between the upper and lower steady-states. This discontinuity acts as part of an ideal IM-wave and moves in the direction of the electric field at a speed U = \sqrt{v_{IM} {+} v_{IM} {-}}, which is the geometric mean of v_{IM} evaluated immediately to the left and right of the discontinuity. This widening speed is typically several hundreds of metres per second. If electron inertial effects are included in the magnetosphere, then the discontinuity is smoothed, and a series of undershoots and overshoots develops behind it. These undershoots and overshoots evolve as inertial IM-waves. Initially they are weakly inertial, with a wavelength of about λ_{e}, however, strong gradients of ω_{IM} cause IM-waves to phase-mix, making their wavelength inversely proportional to time. Therefore, the waves rapidly become strongly inertial and oscillate at ω_{IM}. The inertial IM-waves drive upgoing Alfvén waves in the magnetosphere, which populate a region over the downward current channel, close to its edge. In this manner, the E-region depletion mechanism, that we have detailed, creates small-scale Alfvén waves in large-scale current systems, with properties determined by MI-coupling.
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Moeketsi, Daniel Mojalefa. "Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa." Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005275.
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The South African Global Navigation Satellite System (GNSS) network of dual frequency receivers provide an opportunity to investigate solar cycle effects on ionospheric Total Electron Content (TEC) over the South Africa region by taking advantage of the dispersive nature of the ionospheric medium. For this task, the global University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was adopted, modified and applied to compute TEC using data from the southern African GNSS Network. TEC values were compared with CODE International GNSS services TEC predictions and Ionosonde-derived TEC (ITEC) measurements to test and validate the UNB-IMT results over South Africa. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show pronounced seasonal variations with high TEC values around equinoxes for a year near solar maximum and less pronounced around solar minimum. Signature TEC depletions and enhanced spikes were prevalently evident around equinoxes, particularly for a year near solar maximum. These observations were investigated and further discussed with an analysis of the midday Disturbance Storm Time (DST) index of geomagnetic activity. The residual GTEC – ITEC corresponding to plasmaspheric electron content and equivalent ionospheric foF2 and total slab thickness parameters were computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for ionospheric research over South Africa. The UNB-IMT algorithm was applied to investigate TEC variability during different epochs of solar cycle 23. The results were investigated and further discussed by analyzing the GOES 8 and 10 satellites X-ray flux (0.1 – 0.8 nm) and SOHO Solar Extreme Ultraviolet Monitor higher resolution data. Comparison of UNB-IMT TEC derived from collocated HRAO and HARB GNSS receivers was undertaken for the solar X17 and X9 flare events, which occurred on day 301, 2003 and day 339, 2006. It was found that there exist considerable TEC differences between the two collocated receivers with some evidence of solar cycle dependence. Furthermore, the daytime UNB TEC compared with the International Reference Ionosphere 2001 predicted TEC found both models to show a good agreement. The UNB-IMT TEC was further applied to investigate the capabilities of geodetic Very Long Baseline Interferometry (VLBI) derived TEC using the Vienna TEC Model for space weather monitoring over HartRAO during the CONT02 and CONT05 campaigns conducted during the years 2002 (near solar maximum) and 005 (near solar minimum). The results verified the use of geodetic VLBI as one of the possible instruments for monitoring space weather impacts on the ionosphere over South Africa.
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Shi, Xueling. "Occurrence Statistics and Driving Mechanisms of Ionospheric Ultra-Low Frequency Waves Observed by SuperDARN Radars." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100904.
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Ultra-low frequency (ULF; 1 mHz - 1 Hz) waves are known to play an important role in the transfer of energy from the solar wind to Earth's magnetosphere and ionosphere. The Super Dual Auroral Radar Network (SuperDARN) is an international network consisting of 35 low-power high frequency (HF: 3-30 MHz) coherent scatter radars at middle to polar latitudes that look into Earth's upper atmosphere and ionosphere. In this study, we use Doppler velocity measurements obtained by the SuperDARN radars and coordinated spacecraft observations to investigate the occurrence statistics and driving mechanisms of ionospheric ULF waves. We begin in Chapter 2 with a case study of Pi2 pulsations which are short-duration (5-15 min) damped geomagnetic field oscillations with periods of 40-150 s. Simultaneous observations of Pi2 pulsations from THEMIS spacecraft, midlatitude SuperDARN radars, and ground magnetometers, together with analysis of their longitudinal polarization pattern and azimuthal phase propagation, confirmed that they are consistent with a plasmaspheric virtual resonance excited by a longitudinally localized source near midnight. In Chapter 3, to further investigate the overall occurrence of ionospheric ULF signatures, a comprehensive statistical study was conducted using an automated detection algorithm to identify ionospheric signatures of Pc3-4 and Pc5 waves over 7 years of high time resolution SuperDARN radar data. Specifically, we have investigated their spatial occurrence, frequency characteristics, seasonal factors, and dependence on solar wind and geomagnetic conditions. We note two particular findings: (i) an internal wave-particle interaction source is most likely responsible for Pc4 waves at high latitudes in the duskside ionosphere; and, (ii) a source associated with magnetotail dynamics during active geomagnetic times is suggested for Pc3-4/Pi2 waves at midlatitudes in the nightside ionosphere. These findings are further expanded in Chapter 4 which investigates the hypothesis that internal wave-particle interactions are an important source for generation of these waves. A case study of long-lasting poloidal waves was conducted using coordinated observations with the GOES and THEMIS satellites to examine the generation and propagation of waves observed in the dayside ionosphere by multiple SuperDARN radars. The source of wave excitation is suggested to be bump-on-tail ion distributions at 1-3 keV. Collectively, these research findings provide better constraints on where and when ionospheric ULF waves occur, their source mechanisms, and how they might affect magnetospheric and ionospheric dynamics.Doctor of Philosophy
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Starks, Michael James 1971. "Measurement of the conjugate propagation of VLF waves by matched filter and application to ionospheric diagnosis." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80126.
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Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.Includes bibliographical references (p. 173-176).
by Michael James Starks.
Sc.D.
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Pradipta, Rezy. "Generation of acoustic-gravity waves in ionospheric HF heating experiments : simulating large-scale natural heat sources." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/79031.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 203-208).
In this thesis, we investigate the potential role played by large-scale anomalous heat sources (e.g. prolonged heat wave events) in generating acoustic-gravity waves (AGWs) that might trigger widespread plasma turbulence in the ionospheric layer. The main hypothesis is that, the thermal gradients associated with the heat wave fronts could act as a source of powerful AGW capable of triggering ionospheric plasma turbulence over extensive areas. In our investigations, first we are going to examine a case study of the summer 2006 North American heat wave event. Our examination of GPS-derived total electron content (TEC) data over the North American sector reveals a quite noticeable increase in the level of daily plasma density fluctuations during the summer 2006 heat wave period. Comparison with the summer 2005 and summer 2007 data further confirms that the observed increase of traveling ionospheric disturbances (TIDs) during the summer 2006 heat wave period was not simply a regular seasonal phenomenon. Furthermore, a series of field experiments had been carried out at the High-frequency Active Auroral Research Program (HAARP) facility in order to physically simulate the process of AGW/TID generation by large-scale thermal gradients in the ionosphere. In these ionospheric HF heating experiments, we create some time-varying artificial thermal gradients at an altitude of 200-300 km above the Earth's surface using vertically-transmitted amplitude-modulated 0-mode HF heater waves. For our experiments, a number of radio diagnostic instruments had been utilized to detect the characteristic signatures of heater-generated AGW/TID. So far, we have been able to obtain several affirmative indications that some artificial AGW/TID are indeed being radiated out from the heated plasma volume during the HAARP-AGW experiments. Based on the experimental evidence, we may conclude that it is certainly quite plausible for large-scale thermal gradients associated with severe heat wave events to generate some AGW which might induce widespread plasma turbulence far in space.
by Rezy Pradipta.
Ph.D.
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Ivchenko, Nickolay. "Alfven Waves and Spatio-Temporal Structuring in the Auroral Ionosphere." Doctoral thesis, KTH, Alfvénlaboratoriet, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3364.
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Norin, Lars. "Secondary Electromagnetic Radiation Generated by HF Pumping of the Ionosphere." Doctoral thesis, Uppsala universitet, Astronomi och rymdfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9393.
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Electromagnetic waves can be used to transmit information over long distances and are therefore often employed for communication purposes. The electromagnetic waves are reflected off material objects on their paths and interact with the medium through which they propagate. For instance, the plasma in the ionosphere can refract and even reflect radio waves propagating through it. By increasing the power of radio waves injected into the ionosphere, the waves start to modify the plasma, resulting in the generation of a wide range of nonlinear processes, including turbulence, in particular near the reflection region. By systematically varying the injected radio waves in terms of frequency, power, polarisation, duty cycle, inclination, etc. the ionosphere can be used as an outdoor laboratory for investigating fundamental properties of the near-Earth space environment as well as of plasma turbulence. In such ionospheric modification experiments, it has been discovered that the irradiation of the ionosphere by powerful radio waves leads to the formation of plasma density structures and to the emission of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission. These processes are highly repeatable and have enabled systematic investigations of the nonlinear properties of the ionospheric plasma. In this thesis we investigate features of the plasma density structures and the secondary electromagnetic radiation. In a theoretical study we analyse a certain aspect of the formation of the plasma structures. The transient dynamics of the secondary radiation is investigated experimentally in a series of papers, focussing on the initial stage as well as on the decay. In one of the papers we use the transient dynamics of the secondary radiation to reveal the intimate relation between certain features of the radiation and structures of certain scales. Further, we present measurements of unprecedentedly strong secondary radiation, attributed to stimulated Brillouin scattering, and report measurements of the secondary radiation using a novel technique imposed on the transmitted radio waves.
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Kim, Tony C. "Interaction of Very Low Frequency (VLF) and Extremely Low Frequency (ELF) Waves in the Ionospheric Plasma and Parametric Antenna Concept." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1486674973747427.
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Hall, Jan-Ove. "Interaction between Electromagnetic Waves and Localized Plasma Oscillations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4282.
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Nordblad, Erik. "Opening New Radio Windows and Bending Twisted Beams." Doctoral thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158797.
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In ground based high frequency (HF) radio pumping experiments, absorption of ordinary (O) mode pump waves energises the ionospheric plasma, producing optical emissions and other effects. Pump-induced or natural kilometre-scale field-aligned density depletions are believed to play a role in self-focussing phenomena such as the magnetic zenith (MZ) effect, i.e., the increased plasma response observed in the direction of Earth's magnetic field. Using ray tracing, we study the propagation of ordinary (O) mode HF radio waves in an ionosphere modified by density depletions, with special attention to transmission through the radio window (RW), where O mode waves convert into the extraordinary (X, or Z) mode. The depletions are shown to shift the position of the RW, or to introduce RWs at new locations. In a simplified model neglecting absorption, we estimate the wave electric field strength perpendicular to the magnetic field at altitudes normally inaccessible. This field could excite upper hybrid waves on small scale density perturbations. We also show how transmission and focussing combine to give stronger fields in some directions, notably at angles close to the MZ, with possible implications for the MZ effect. In a separate study, we consider electromagnetic (e-m) beams with helical wavefronts (i.e., twisted beams), which are associated with orbital angular momentum (OAM). By applying geometrical optics to each plane wave component of a twisted nonparaxial e-m Bessel beam, we calculate analytically the shift of the beam's centre of gravity during propagation perpendicularly and obliquely to a weak refractive index gradient in an isotropic medium. In addition to the so-called Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions. In some situations, the new shifts should be significant also for nearly paraxial beams.
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De, Larquier Sebastien. "The mid-latitude ionosphere under quiet geomagnetic conditions: propagation analysis of SuperDARN radar observations from large ionospheric perturbations." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24770.
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The Earth's ionosphere is a dynamic environment strongly coupled to the neutral atmosphere, magnetosphere and solar activity. In the context of this research, we restrict our interest to the mid-latitude (a.k.a., sub-auroral) ionosphere during quiet geomagnetic conditions. The Super Dual Auroral Radar Network (SuperDARN) is composed of more than 30 low-power High Frequency (HF, from 8-18 MHz) Doppler radars covering the sub-auroral, auroral and polar ionosphere in both hemispheres. SuperDARN radars rely on the dispersive properties of the ionosphere at HF to monitor dynamic features of the ionosphere. Though originally designed to follow auroral expansion during active periods, mid-latitude SuperDARN radars have observed ground and ionospheric scatter revealing several interesting features of the mid-latitude ionosphere during periods of moderate to low geomagnetic activity. The past 7 years' expansion of SuperDARN to mid-latitudes, combined with the recent extended solar minimum, provides large-scale continuous views of the sub-auroral ionosphere for the first time. We have leveraged these circumstances to study prominent and recurring features of the mid-latitude ionosphere under quiet geomagnetic conditions.
First, we seek to establish a better model of HF propagation effects on SuperDARN observations. To do so, we developed a ray-tracing model coupled with the International Reference Ionosphere (IRI). This model is tested against another well established ray-tracing model, then optimized to be compared to SuperDARN observations (Chapter 2).
The first prominent ionospheric feature studied is an anomaly in the standard ionospheric model of photo-ionization and recombination. This type of event provides an ideal candidate for testing the ray-tracing model and analyzing propagation effects in SuperDARN observations. The anomaly was first observed in ground backscatter occurring around sunset for the Blackstone, VA SuperDARN radar. We established that it is related to an unexpected enhancement in electron densities that leads to increased refraction of the HF signals. Using the ray-tracing, IRI model, and measurements from the Millstone Hill Incoherent Scatter Radar (ISR), we showed that this enhancement is part of a global phenomenon in the Northern Hemisphere, and is possibly related to the Southern Hemisphere's Weddell Sea Anomaly. We also tested a potential mechanism involving thermospheric winds and geomagnetic field configuration which showed promising results and will require further modeling to confirm (Chapter 3).
The second ionospheric feature was a type of decameter-scale irregularity associated with very low drift velocities. Previous work had established that these irregularities occur throughout the year, during nighttime, and equatorward of both the auroral regions and the plasmapause boundary. An initial analysis suggested that the Temperature Gradient Instability (TGI) was responsible for the growth of such irregularities. We first used our ray-tracing model to distinguish between HF propagation effects and irregularity occurrence in SuperDARN observations. This revealed the irregularities to be widespread within the mid-latitude ionosphere and located in the bottom-side F-region (Chapter 4). A second study using measurements from the Millstone Hill ISR revealed that TGI driven growth was possible but only in the top-side F-region ionosphere. We found that initial growth may occur primarily at larger wavelengths, with subsequent cascade to decameter-scale with coupling throughout the F-region (Chapter 5).
In summary, the research conducted during this PhD program has established a robust method to analyze quiet-time SuperDARN observations. It also furthered our physical understanding of some prominent features of the mid-latitude ionosphere. It leaves behind a flexible ray-tracing model, multiple online tools to browse SuperDARN data, and a thorough and growing Space Science API providing access to multiple datasets, models and visualization tools.Ph. D.
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Barabash, Victoria. "Investigation of Polar Mesosphere Summer Echoes in Northern Scandinavia." Doctoral thesis, Umeå University, Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-176.
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This PhD thesis deals with phenomena which are closely related to the unique thermal structure of the polar summer mesosphere, namely Polar Mesosphere Summer Echoes (PMSE). PMSE are strong radar echoes commonly observed by VHF MST radars from thin layers in the 80-90 km altitude interval at high latitudes during summer. They follow a seasonal pattern of abrupt appearance in late May and a gradual disappearance in mid-August. This period corresponds roughly to the time between the completion of the summer time cooling of the polar mesopause to the time of reversal of the mesospheric circulation to autumn condition. In this connection, PMSE are associated with the extremely low temperatures, i.e. below 140 K, which are unique to the polar summer mesopause. Traditional theories of radar (partial) reflection and scattering have been unable to explain the PMSE and the exact mechanism for their occurrence remains unclear despite the steadily increasing interest in them over the past 20 years. Currently accepted theories regarding the mechanism giving rise to PMSE agree that one of the conditions needed for enhanced radar echoes is the presence of low-mobility charge carries such as large cluster ions and ice aerosols which capture the ambient electrons. It has been established that the PMSE are in some way associated with noctilucent clouds (NLC), layers of ice crystals, which constitute the highest observed clouds in the earth’s atmosphere. PMSE occurrence and dynamics are also found to be closely connected with the planetary and gravity waves.
Observations of PMSE presented in this thesis have been carried out by the Esrange MST radar (ESRAD) located at Esrange (67°56’N, 21°04’E) just outside Kiruna in northernmost Sweden. The radar operates at 52 MHz with 72 kW peak power and a maximum duty cycle of 5%. The antenna consists of 12x12 array of 5-element Yagis with a 0.7l spacing. During the PMSE measurements the radar used a 16-bit complementary code having a baud length of 1mS. This corresponds to height resolution of 150 m. The sampling frequency was set at 1450 Hz. The covered height range was 80-90 km. The presence of PMSE was determined on the basis of the radar SNR (signal-to-noise ratio). The PMSE measurements have been made during May-August each year since 1997.
PMSE seasonal and diurnal occurrence rates as well as dynamics have been studied in connection with tidal winds, planetary waves, temperature and water vapor content in the mesosphere (Papers I, IV and VI). Simultaneous and common-volume observations of PMSE and noctilucent clouds have been performed by radar, lidar and CCD camera (Paper V). Correlation between variations in PMSE and variations in extra ionization added by precipitating energetic electrons or high-energy particles from the Sun has been examined (Papers II and III). Possible influence of transport effects due to the electric field on PMSE appearance has been studied during a solar proton event (Paper III).
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Oronsaye, Samuel Iyen Jeffrey. "Updating the ionospheric propagation factor, M(3000)F2, global model using the neural network technique and relevant geophysical input parameters." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001609.
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This thesis presents an update to the ionospheric propagation factor, M(3000)F2, global empirical model developed by Oyeyemi et al. (2007) (NNO). An additional aim of this research was to produce the updated model in a form that could be used within the International Reference Ionosphere (IRI) global model without adding to the complexity of the IRI. M(3000)F2 is the highest frequency at which a radio signal can be received over a distance of 3000 km after reflection in the ionosphere. The study employed the artificial neural network (ANN) technique using relevant geophysical input parameters which are known to influence the M(3000)F2 parameter. Ionosonde data from 135 ionospheric stations globally, including a number of equatorial stations, were available for this work. M(3000)F2 hourly values from 1976 to 2008, spanning all periods of low and high solar activity were used for model development and verification. A preliminary investigation was first carried out using a relatively small dataset to determine the appropriate input parameters for global M(3000)F2 parameter modelling. Inputs representing diurnal variation, seasonal variation, solar variation, modified dip latitude, longitude and latitude were found to be the optimum parameters for modelling the diurnal and seasonal variations of the M(3000)F2 parameter both on a temporal and spatial basis. The outcome of the preliminary study was applied to the overall dataset to develop a comprehensive ANN M(3000)F2 model which displays a remarkable improvement over the NNO model as well as the IRI version. The model shows 7.11% and 3.85% improvement over the NNO model as well as 13.04% and 10.05% over the IRI M(3000)F2 model, around high and low solar activity periods respectively. A comparison of the diurnal structure of the ANN and the IRI predicted values reveal that the ANN model is more effective in representing the diurnal structure of the M(3000)F2 values than the IRI M(3000)F2 model. The capability of the ANN model in reproducing the seasonal variation pattern of the M(3000)F2 values at 00h00UT, 06h00UT, 12h00UT, and l8h00UT more appropriately than the IRI version is illustrated in this work. A significant result obtained in this study is the ability of the ANN model in improving the post-sunset predicted values of the M(3000)F2 parameter which is known to be problematic to the IRI M(3000)F2 model in the low-latitude and the equatorial regions. The final M(3000)F2 model provides for an improved equatorial prediction and a simplified input space that allows for easy incorporation into the IRI model.
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Botai, Ondego Joel. "Ionospheric total electron content variability and its influence in radio astronomy." Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005258.
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Ionospheric phase delays of radio signals from Global Positioning System (GPS) satellites have been used to compute ionospheric Total Electron Content (TEC). An extended Chapman profle model is used to estimate the electron density profles and TEC. The Chapman profle that can be used to predict TEC over the mid-latitudes only applies during day time. To model night time TEC variability, a polynomial function is fitted to the night time peak electron density profles derived from the online International Reference Ionosphere (IRI) 2001. The observed and predicted TEC and its variability have been used to study ionospheric in°uence on Radio Astronomy in South Africa region. Di®erential phase delays of the radio signals from Radio Astronomy sources have been simulated using TEC. Using the simulated phase delays, the azimuth and declination o®sets of the radio sources have been estimated. Results indicate that, pointing errors of the order of miliarcseconds (mas) are likely if the ionospheric phase delays are not corrected for. These delays are not uniform and vary over a broad spectrum of timescales. This implies that fast frequency (referencing) switching, closure phases and fringe ¯tting schemes for ionospheric correction in astrometry are not the best option as they do not capture the real state of the ionosphere especially if the switching time is greater than the ionospheric TEC variability. However, advantage can be taken of the GPS satellite data available at intervals of a second from the GPS receiver network in South Africa to derive parameters which could be used to correct for the ionospheric delays. Furthermore GPS data can also be used to monitor the occurrence of scintillations, (which might corrupt radio signals) especially for the proposed, Square Kilometer Array (SKA) stations closer to the equatorial belt during magnetic storms and sub-storms. A 10 minute snapshot of GPS data recorded with the Hermanus [34:420 S, 19:220 E ] dual frequency receiver on 2003-04-11 did not show the occurrence of scintillations. This time scale is however too short and cannot be representative. Longer time scales; hours, days, seasons are needed to monitor the occurrence of scintillations.
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黃元華 and Yuen-wah Wong. "A study of atomospheric gravity waves in East Asia by investigation oftheir effects upon the ionosphere." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31232875.
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Wong, Yuen-wah. "A study of atomospheric gravity waves in East Asia by investigation of their effects upon the ionosphere /." [Hong Kong : University of Hong Kong], 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13148424.
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Mercer, Christopher Crossley. "The search for an ionospheric model suitable for real-time applications in HF radio communications." Thesis, Rhodes University, 1994. http://hdl.handle.net/10962/d1005274.
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Statement of work: In essence the research work was to focus on the development of an ionospheric model suitable for real time HF frequency prediction and direction finding applications. The modelling of the ionosphere had to be generic in nature, sufficient to ensure that the CSIR could simultaneously secure commercial competitiveness in each of the three niche market areas aforementioned, while requiring only minimal changes to software architecture in the case of each application. A little research quickly showed that the development of an ionospheric model capable of driving a HFDFSSL system in "real time" would result in one having to make only slight re-structuring of the software to facilitate application of the same model in the areas of real time frequency prediction and spectrum management. The decision made at the outset of the project to slant the research toward the development of a model best suited for HF direction finding applications is reflected in the avenues followed during the course of the modelling process
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Carozzi, Tobia. "Radio waves in the ionosphere : Propagation, generation and detection." Doctoral thesis, Uppsala universitet, Institutionen för astronomi och rymdfysik, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1184.
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We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma.With regards to generation, we will be concerned with three experiments con-ducted at the ionosphere- radio wave interaction research facilities at Sura, Rus-siaand Tromsø, Norway. These facilities operate high power HF transmittersthat can inject large amplitude electromagnetic waves into the ionosphere andexcite numerous nonlinear processes. In an experiment conducted at the Surafacility, we were able to measure the full state of polarization of stimulatedelectromagnetic emissions for the first time. It is expected that by using thetechnique developed in this experiment it will be possible to study nonlinearpolarization effects on powerful HF pump waves in magnetoplasmas in the fu-ture.In another experiment conducted at the Sura facility, the pump frequencywas swept automatically allowing rapid, high-resolution measurements of SEEdependence on pump frequency with minimal variations in ionospheric condi-tions.At the Tromsø facility we discovered by chance a highly variable, pumpinduced, HF emission that most probably emanated from pump excited spo-radicE. Regarding detection, we have proposed a set of Stokes parametersgeneralized to three dimension space; and we have used these parameters in aninvention to detect the incoming direction of electromagnetic waves of multiplefrequencies from a single point measurement.
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Bond, Giles Edward. "The interaction of radio waves with the auroral ionosphere." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30629.
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A high power radio wave propagating through the ionosphere perturbs the natural plasma in a number of ways. These include bulk changes in the electron temperature and density, and the excitation of plasma waves and instabilities. The ionosphere can be regarded as a natural plasma laboratory, with far greater scale sizes then anything achievable in a conventional laboratory, thus giving unique access to a range of plasma waves and instabilities. In this thesis results from two campaigns involving the EISCAT (European Incoherent SCATter) ionospheric modification facility (heater) at Tromso, Northern Norway are presented. The first campaign, in February 1995, was principally concerned with modification of the auroral electrojet region during both disturbed and quiet conditions. During this campaign the EISCAT UHF incoherent scatter radar was utilised to achieve the first experimental demonstration of artificial inospheric cooling by a high power radio wave. For the second campaign, in April 1996, the most important diagnostic was CUTLASS (Co-operative UK Twin Located Auroral Sounding System), which can measure power backscattered from field aligned irregularities produced during heating. It has been found that irregularities are excited over a horizontal spatial extent of around 175 km, which far exceeds the normal width of the heater beam. The temporal decay of artificial irregularities remain in the ionosphere for up to four minutes after heater-off. In addition to these experimental studies, a computer model has been developed to investigate the electron temperature and density changes which are induced in the ionospheric D- and E-regions during periods of electrojet activity. The model reproduces the experimental observations, and predicts reduced artificial heating efficiency under distributed natural conditions.
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Carozzi, Tobia D. "Radio waves in the ionosphere : propagation, generation, and detection /." Uppsala : Institutionen för astronomi och rymdfysik, Univ. [distributör], 2000. http://publications.uu.se/theses/99-3364278-2/.
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Hoffmann, Peter, and Christoph Jacobi. "Connection of Planetary Waves in the Stratosphere and Ionosphere by the Modulation of Gravity Waves." Universität Leipzig, 2010. https://ul.qucosa.de/id/qucosa%3A16359.
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A possible connection of planetary waves (PW) and ionospheric planetary wave type oscillations (PWTO) at midlatitudes is studied by analyzing MetOffice stratospheric reanalysis data and maps of the Total Electron Content. Although the seasonal variability looks similar, the vertical coupling between stratosphere and ionosphere is known to only happen indirectly through processes such as the modulation of gravity waves (GW) by
PW. To investigate possible coupling processes, information about GW are retrieved from SABER temperature profiles (30-130 km) by calculating the potential energy (Ep) and generating daily maps of Ep. For the period of time from 2003-07-19 to 2005-07-20 proxies of stationary and travelling PW were calculated to obtain a general picture of PW activity, modulation of GW by PW and activity of PWTO in the ionosphere. The results reveals that mostly PW itself cannot reach lower thermospheric heights, but their signatures propagate upward up to 120 km and above, where they can trigger PWTO.Ein möglicher Zusammenhang zwischen dem Auftreten planetarer Wellen (PW) und typischer Oszillationen planetarer Wellen (PWTO) der Ionosphäre in mittleren Breiten wird auf der Basis von Analysen stratosphärischer Reanalysen und Karten des Gesamtelektronengehalts untersucht. Obwohl das saisonale Verhalten ähnlich erscheint, kann die Kopplung nur auf indirektem Wege erfolgen, wie z.B. durch die Modulation von Schwerewellen (GW) durch PW. Die für die Analysen notwendigen Informationen über GW können aus Temperaturprofilen (30-130 km), abgeleitet von Satellitenbeobachtungen (z.B. SABER), durch die Bestimmung der potentiellen Energie von GW, gewonnen werden. Zusammengefasst in täglichen Daten (2003-07-19 to 2005-07-20) stellen Proxies stationärer und wandernder PW ein vereinfachtes Bild des Prozesses der Modulation durch PW dar. Die Ergebnisse zeigen, dass sich PW selbst nicht bis in die unteren Thermosphäre ausbreiten können. Jedoch die Signatur, getragen durch GW, könnte auf diesem Wege als PWTO abgebildet werden.
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Hahlin, Axel. "Coupled waves as a model to describe chaotic turbulence pumped by radio waves in the ionosphere." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-356265.
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Experimental results concerning plasma turbulence pumped in theionosphere by powerful radio waves suggest that the turbulence is due todeterministic chaos. To investigate the possibility of deterministic chaosin the ionosphere coupled wave systems have been studied to see chaoticdynamics. If coupled waves can exhibit chaos it is a possible way tomodel ionospheric chaos. The result showed that chaos was present inboth wave systems studied which means that they could possibly explainthe chaos, to verify this more studies needs to be done on theparameters relevant to the coupled wave systems in the ionosphere andfind if they are in a regime where chaos developsStudier av plasmaturbulens i jonosfären som pumpas av kraftfulla radiovågor antyder att turbulensen är kopplat till deterministiskt kaos. För att undersöka möjligheten för deterministiskt kaos i jonosfären studeras kopplade vågsystem om de kan innehålla kaotiska regimer. Om dessa system visar kaotiskt beteende skulle de kunna användas för att beskriva kaos i jonosfären. Resultatet visade att kaos var närvarande i de kopplade vågsystem som studerats, för att verifiera om de kan användas för att beskriva kaos i jonosfären måste närmare studier av de parametrar som modellen använder sig av göras för att se om de faller inom ett intervall där kaos uppstår.
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Hoffmann, Peter. "Planetary Wave Coupling between Stratosphere and Ionosphere by Gravity Wave Modulation." Doctoral thesis, Universitätsbibliothek Leipzig, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-71533.
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The ionosphere-thermosphere can be considered to a certain degree as a system, which is externally-driven by the extreme-ultraviolet solar radiation. The main components in the regular variation are connected to the solar cycle, solar rotation and the diurnal cycle. However, anomalies and periodicities of several days, which cannot be related to changes in the solar activity at all times, were detected in ionospheric parameters. It is assumed that the total variation in the ionosphere is partly forced by waves coming from below. This thesis provides a clearer picture of the seasonal changes of wave phenomena observed in the ionosphere and its possible relation to lower atmospheric structures. Since such global disturbances in the middle atmosphere are termed as planetary waves (PW), such features in the ionosphere are declared as planetary wave type oscillations (PWTO), although a direct connection is excluded.Northern hemispheric maps of the Total Electron Content (TEC) derived from GPS-signals that are currently used for monitoring the ionospheric F-region in relation to space weather provide a basis for investigating PWTO applying space-time analysis methods to separate stationary and traveling wave components from the data. Compared to analyses of PW obtained by regular stratospheric reanalyses the seasonal behavior and possible coexisting wave activities during the considered period of time (2002-2008) are presented. Such a climatological consideration has revealed that recurring events in the course of the solar cycle are rare, but it seems that the westward propagating quasi 16-day wave with zonal wavenumber 1, analysed from stratospheric MetO reanalyses, and the ionosphere are indirectly coupled. Generally, the correspondence of other components are restricted around the solar maximum 2002-2005. There are some suggestions, how the middle and upper atmosphere are connected by PW. Sounding of the middle atmosphere by remote sensing techniques from satellites (e.g. SABER on TIMED) deliver a suitable basis to investigate the coupling by the modulation of gravity waves (GW). By calculating the potential energy for a certain wave spectrum, characterized by vertical wavelength shorter than 6 km, and determining proxies of traveling waves permits to investigate a possible mechanism. The results reveal that GW partly penetrate the lower thermosphere carrying a modulation by PW. In some cases, especially during the first three winter, near solar maximum, stratospheric PW show a good correlation to indirect signals in the lower thermosphere and to PWTO in the ionospheric F-region near 300 km.
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Stocker, Alan John. "Modification of the ionosphere by means of high power radio waves." Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/35799.
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Experiments have been performed at Troms?, Norway and Arecibo, Puerto Rico to investigate the effects produced by high power radio waves (heating) on the high and low latitude ionospheres, respectively. The modifications induced in the F-region have been observed with both incoherent scatter radars and tow power HF diagnostic radio waves. These observations provide information on both heater-induced large scale changes, and small scale density structures. The spatial and temporal development of the perturbation in electron temperature caused by heating, measured at Troms? for the first time, compares well with theory. Observations of thermal striations, which may be the result of the thermal self-focussing of the heater wave, are also presented. The large-scale heater-induced changes in the electron density measured by EISCAT have been compared with those derived from measurements of the phase of reflected HF diagnostic signals. Both methods yield consistent results with regard to whether the electron density is enhanced or depleted but there are, however, differences in the magnitudes of the measured changes. The sign of the perturbation can reveal aeronomical information on the chemical and diffusion characteristics of the unheated ionosphere. The first observations of tow latitude heating by means of low power HF diagnostic waves are presented. The anomalous absorption measured at tow latitudes is less than that at high latitudes, in agreement with theory. The scale length and amplitude of the associated small-scale density structures are comparable at both high and low latitudes. A detailed comparison has been undertaken of the effect of heating at high and low latitudes and the results compared with current theoretical models. The two independent diagnostic techniques (incoherent scatter and low power HF waves) provide a consistent picture of the ionospheric perturbation induced by both heating facilities.
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Garg, Vidur. "Swept Neutral Pressure Instrument (SNeuPI): Investigating Gravity Waves In The Ionosphere." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/56592.
Full textAbstract:
A swept neutral pressure instrument(SNeuPI) is used to study the effect of gravity waves on the composition of the ionosphere. When mounted on a nanosatellite in the low earth orbit, changes in atmospheric pressure due to gravity waves are measured as the changes in neutral gas density. This measurement is achieved by use of micro-tip emitters as an electron source and micro channel plates(MCPs) as ion collectors. Ionization of the neutral gas produces a current at the output of the MCPs to quantify the pressure of the ionosphere. Traditionally, such measurements are made on larger satellites which enable the use of higher power equipment. This thesis describes the design and use of a low power instrument, to be used on a limited-resource satellite. The background and theoretical analysis is presented first, followed by descriptions of the mechanical and electrical designs. The laboratory tests are limited to a vacuum chamber setup that simulates the conditions of the ionosphere.Master of Science
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Hoffmann, Peter, and Christoph Jacobi. "Response of the ionospheric total electron content to stratospheric normal modes." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-223214.
Full textAbstract:
Globale Karten des totalen Elektronengehaltes (TEC) der Ionosphäre werden nach Signalen planetarer Wellenaktivität aus der Stratosphäre im Bereich der mittleren Breiten (ca. 52.5° N) untersucht, um eine Abschätzung über die vertikale Kopplung durch planetare Wellen (PW) zu erhalten. Die Variabilität der Ionosphäre wird operationell durch das DLR Neustrelitz erfasst. Seit 2002 werden zu diesem Zwecke hemisphärische TEC Karten erstellt, die eine Analyse PW typischer Oszillationen in der Ionosphäre ermöglichen. Die verwendete Methode zur Analyse separiert Wellen nach ihrer zonalen Wellenzahl, Periode und Ausbreitungsrichtung. In einer vorherigen Fallstudie vom Herbst 2004 wurde u.a. die quasi 6-Tage Welle (m2w) im mittleren Spektrum für das Geopotential in 1hPa (Stratosphäre) als auch den ionosphärischen TEC beobachtet. Die aktuellen Resultate geben Hinweise für ein gleichzeitiges Auftreten dieserWelle mit einer quasi 6-Tage Oszillation in der Mesopausenregion. Jedoch im Vergleich zur Stratosphäre scheinen die Signaturen verschoben und etwas modifiziertThe response of stratospheric planetary wave (PW) activity over the higher middle latitudes (ca. 52.5° N) in global gridded ionospheric data of the total electron content (TEC) are investigated to estimate the vertical coupling by PW. The monitoring of ionospheric variability is regularly operated by DLR Neustrelitz since 2002 producing TEC maps covering the northern hemisphere. This data base is considered for comparing simultaneous observations of wave activity in both stratosphere and ionosphere. The analysis technique of planetary wave type oscillations (PWTO) is carried out by separating waves into their zonal wavenumber, period and travelling direction. A previous case study of autumn 2004 has shown that among other things the quasi 6-day wave (m2w) is visible in the mean spectrum of stratospheric geopotential height at 1 hPa pressure level and of ionospheric TEC data. The actual results give hints for a simultaneous occurrence of this wave type with a quasi 6-day oscillation in the mesopause region. But in comparison to the stratosphere, the wave signatures seem to be somewhat schifted and modified
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Meyer, Melissa G. "Remote sensing of localized ion acoustic waves with multistatic passive radar /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/6062.
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Opperman, B. D. L. "Reconstructing ionospheric TEC over South Africa using signals from a regional GPS network." Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005273.
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Radio signals transmitted by GPS satellites orbiting the Earth are modulated as they propagate through the electrically charged plasmasphere and ionosphere in the near-Earth space environment. Through a linear combination of GPS range and phase measurements observed on two carrier frequencies by terrestrial-based GPS receivers, the ionospheric total electron content (TEC) along oblique GPS signal paths may be quantified. Simultaneous observations of signals transmitted by multiple GPS satellites and observed from a network of South African dual frequency GPS receivers, constitute a spatially dense ionospheric measurement source over the region. A new methodology, based on an adjusted spherical harmonic (ASHA) expansion, was developed to estimate diurnal vertical TEC over the region using GPS observations over the region. The performance of the ASHA methodology to estimate diurnal TEC and satellite and receiver differential clock biases (DCBs) for a single GPS receiver was first tested with simulation data and subsequently applied to observed GPS data. The resulting diurnal TEC profiles estimated from GPS observations compared favourably to measurements from three South African ionosondes and two other GPS-based methodologies for 2006 solstice and equinox dates. The ASHA methodology was applied to calculating diurnal two-dimensional TEC maps from multiple receivers in the South African GPS network. The space physics application of the newly developed methodology was demonstrated by investigating the ionosphere’s behaviour during a severe geomagnetic storm and investigating the long-term ionospheric stability in support of the proposed Square Kilometre Array (SKA) radio astronomy project. The feasibility of employing the newly developed technique in an operational near real-time system for estimating and dissimenating TEC values over Southern Africa using observations from a regional GPS receiver network, was investigated.
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Cannon, Patrick. "Numerical simulation of wave-plasma interactions in the ionosphere." Thesis, Lancaster University, 2016. http://eprints.lancs.ac.uk/80076/.
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Ionospheric modification by means of high-power electromagnetic (EM) waves can result in the excitation of a diverse range of plasma waves and instabilities. This thesis presents the development and application of a GPU-accelerated finite-difference time-domain (FDTD) code designed to simulate the time-explicit response of an ionospheric plasma to incident EM waves. Validation tests are presented in which the code achieved good agreement with the predictions of plasma theory and the computations of benchmark software. The code was used to investigate the mechanisms behind several recent experimental observations which have not been fully understood, including the effect of 2D density inhomogeneity on the O-mode to Z-mode conversion process and thus the shape of the conversion window, and the influence of EM wave polarisation and frequency on the growth of density irregularities. The O-to-Z-mode conversion process was shown to be responsible for a strong dependence of artificially-induced plasma perturbation on both the EM wave inclination angle and the 2D characteristics of the background plasma. Allowing excited Z-mode waves to reflect back towards the interaction region was found to cause enhancement of the electric field and a substantial increase in electron temperature. Simulations of O-mode and X-mode polarised waves demonstrated that both are capable of exciting geomagnetic field-aligned density irregularities, particularly at altitudes where the background plasma frequency corresponds to an electron gyroharmonic. Inclusion of estimated electrostatic fields associated with irregularities in the simulation algorithm resulted in an enhanced electron temperature. Excitation of these density features could address an observed asymmetry in anomalous absorption and recent unexplained X-mode heating results reported at EISCAT. Comparing simulations with ion motion allowed or suppressed indicated that a parametric instability was responsible for irregularity production. Simulation of EM wave fields confirmed that X-mode waves are capable of exceeding the threshold for parametric instability excitation under certain conditions.
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Dhillon, Ranvir Singh. "Radar studies of natural and artificial waves and instabilities in the auroral ionosphere." Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/30657.
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The electron Pedersen conductivity instability (EPCI) was proposed by Dimant and Sudan (1995a, 1995b, 1995c) as an extension to accepted Farley-Buneman instability theory and was predicted to give rise to D-region radar echoes. Theoretical modelling of its growth rate and threshold velocity for varying flow and aspect angles is presented, together with evidence for a two-layer structure where the growth rate is maximised. Backscatter parameters obtained by two coherent radar systems, CUTLASS and STARE, are presented for two case studies where the data are consistent with an electrojet flow whose velocity exceeds the threshold value for EPCI excitation. Backscatter parameters obtained from artificially generated FAIs for spatial sweeping and preconditioning experiments are also presented. Varying the illumination time of part of the heated patch affects the CUTLASS backscatter power corresponding to that patch. The variation in backscatter over CUTLASS range gates, for a heater beam with varying pointing direction, is shown to agree closely with the expected results obtained by modelling the heater beam intensity. It is shown that the CUTLASS backscatter power, for a given heater power, is dependent upon whether the ionosphere has previously been excited at a higher heater power. A new longer-lag mode was run on CUTLASS for the October 1999 heating campaign and the ACF decorrelation and backscatter power decay time constants obtained from data collected when this mode was running were different by an order of magnitude. Turbulence characteristics were obtained from the artificial irregularity distribution. These are compared to a study preferred by Villain et al. (1996) and the results are consistent with an artificial irregularity distribution that remained correlated for longer times than naturally occurring irregularity distributions.
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Hoffmann, Peter, and Christoph Jacobi. "Response of the ionospheric total electron content to stratospheric normal modes." Universität Leipzig, 2007. https://ul.qucosa.de/id/qucosa%3A15572.
Full textAbstract:
Globale Karten des totalen Elektronengehaltes (TEC) der Ionosphäre werden nach Signalen planetarer Wellenaktivität aus der Stratosphäre im Bereich der mittleren Breiten (ca. 52.5° N) untersucht, um eine Abschätzung über die vertikale Kopplung durch planetare Wellen (PW) zu erhalten. Die Variabilität der Ionosphäre wird operationell durch das DLR Neustrelitz erfasst. Seit 2002 werden zu diesem Zwecke hemisphärische TEC Karten erstellt, die eine Analyse PW typischer Oszillationen in der Ionosphäre ermöglichen. Die verwendete Methode zur Analyse separiert Wellen nach ihrer zonalen Wellenzahl, Periode und Ausbreitungsrichtung. In einer vorherigen Fallstudie vom Herbst 2004 wurde u.a. die quasi 6-Tage Welle (m2w) im mittleren Spektrum für das Geopotential in 1hPa (Stratosphäre) als auch den
ionosphärischen TEC beobachtet. Die aktuellen Resultate geben Hinweise für ein gleichzeitiges Auftreten dieserWelle mit einer quasi 6-Tage Oszillation in der Mesopausenregion. Jedoch im Vergleich zur Stratosphäre scheinen die Signaturen verschoben und etwas modifiziert.The response of stratospheric planetary wave (PW) activity over the higher middle latitudes (ca. 52.5° N) in global gridded ionospheric data of the total electron content (TEC) are investigated to estimate the vertical coupling by PW. The monitoring of ionospheric variability is regularly operated by DLR Neustrelitz since 2002 producing TEC maps covering the northern hemisphere. This data base is considered for comparing simultaneous observations of wave activity in both stratosphere and ionosphere. The analysis technique of planetary wave type oscillations (PWTO) is carried out by separating waves into their zonal wavenumber, period and travelling direction. A previous case study of autumn 2004 has shown that among other things the quasi 6-day wave (m2w) is visible in the mean spectrum of stratospheric geopotential height at 1 hPa pressure level and of ionospheric TEC data. The actual results give hints for a simultaneous occurrence of this wave type with a quasi 6-day oscillation in the mesopause region. But in comparison to the stratosphere, the wave signatures seem to be somewhat schifted and modified.
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Xi, Hong. "Theoretical and Numerical Studies of Frequency Up-shifted Ionospheric Stimulated Radiation." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29279.
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Stimulated electromagnetic emission (SEE) produced by interactions of high-power radio waves with the Earth's ionosphere is currently a topic of significant interest in ionospheric modification physics. SEE is believed to be produced by nonlinear wave-wave interactions involving the electromagnetic and electrostatic plasma waves in the altitude region where the pump wave frequency is near the upper hybrid resonance frequency. The most prominent upshifted feature in the SEE spectrum is the broad upshifted maximum (BUM). In this study, the instability processes thought to be responsible to the BUM spectra in the SEE experiments are discussed and analyzed using theoretical and electrostatic particle-in-cell (PIC) models.
From characteristics of this feature, a four-wave parametric decay process has been studied as a viable mechanism for its production. The object is to (1) investigate the early time nonlinear development of the four-wave decay instability by using theoretical and numerical simulation models, (2) study the variation of the four-wave decay instability spectral features for a wide range of plasma and pump wave parameters, and (3) access its possible role in the production of the BUM spectral feature. Results of this investigation show that there is good agreement between predictions of the proposed theoretical model and the numerical simulation experiments. The simulation electric field power spectrum exhibits many of the important features of the experimental observations. The numerical simulation results show that consideration of the full nonlinear development of the four-wave parametric instability is crucial in providing insight into the asymmetric nature of the wave frequency spectrum observed during the experiments.
The velocity-space ring-plasma instability, another generation mechanism for the BUM spectra, is studied using a theoretical model. The theoretical calculations show that the growth rate is larger in the region of the upper hybrid wave than that of the electron Bernstein wave. In addition, the effects of various plasma parameters are analyzed and it is predicted that the BUM should be more prominent with a hotter ring, at the direction perpendicular to the magnetic field, or in a closer region of cyclotron harmonic. A detailed comparison of the velocity space ring-plasma instability and the four-wave parametric process is presented where both the differences and the possible relations are discussed.Ph. D.
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Wohlwend, Christian Stephen. "Modeling the Electrodynamics of the Low-Latitude Ionosphere." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/11.
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The electrodynamics of the Earth's low-latitude ionosphere is dependent on the ionospheric conductivity and the thermospheric neutral density, temperature, and winds present. This two-part study focused on the gravity wave seeding mechanism of equatorial plasma depletions in the ionosphere and the associated equatorial spread F, as well as the differences between a two-dimensional flux tube integrated electrodynamics model and a three-dimensional model for the same time period. The gravity wave seeding study was based on a parameterization of a gravity wave perturbation using a background empirical thermosphere and a physics-based ionosphere for the case of 12 UT on 26 September 2002. The electrodynamics study utilized a two-dimensional flux tube integrated model in center dipole coordinates, which is derived in this work. This case study examined the relative influence of the zonal wind, meridional wind, vertical wind, temperature, and density perturbations of the gravity wave. It further looked at the angle of the wave front to the field line flux tube, the most influential height of the perturbation, and the difference between planar and thunderstorm source gravity waves with cylindrical symmetry. The results indicate that, of the five perturbation components studied, the zonal wind is the most important mechanism to seed the Rayleigh-Taylor instability needed to develop plasma plumes. It also shows that the bottomside of the F-region is the most important region to perturb, but a substantial E-region influence is also seen. Furthermore, a wave front with a small angle from the field line is necessary, but the shape of the wave front is not critical in the gravity wave is well developed before nightfall. Preliminary results from the three-dimensional model indicate that the equipotential field line assumption of the two-dimensional model is not valid below 100 km and possibly higher. Future work with this model should attempt to examine more of the differences with the two-dimensional model in the electric fields and currents produced as well as with the plasma drifts that lead to plume development.
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Scoffield, Hannah Clare. "Ultra low frequency waves in the magentosphere-ionosphere system : a joint space- and ground-based investigation." Thesis, University of Leicester, 2005. http://hdl.handle.net/2381/30692.
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This thesis examines the behaviour of large scale magnetohydrodynamic ultra low frequency (ULF) waves in the coupled magnetosphere-ionosphere system. Wave energy from solar wind driven disturbances at the magnetopause, is carried through the magnetosphere by compressional, fast mode waves, which couple to field guided Alfven mode waves on geomagnetic field lines. Field lines with eigenfrequencies corresponding to the driving frequency become resonant. Energy is dissipated in the ionosphere where partial reflection of the Alfven waves takes place, via Joule heating. The general aim of work presented in this thesis is to combine ground based measurements of the large scale structure of individual ULF waves with in-situ measurements of the small scale structure of the electric field, magnetic field and particle precipitation, made by the Fast Auroral SnapshoT (FAST) satellite. With a more specific aim to investigate the small scale structures which give rise to small regions of high current density, leading to parallel electric fields, particle acceleration and aurora. Details of the mechanisms which result in particle acceleration are not fully understood and are of considerable interest at present.;Four field line resonances (FLRs) with conjugate radar, magnetometer and FAST Satellite observations have been studied and compared. In each case a simple FLR model was created and scaled using the wave's spatial and temporal characteristics inferred from SuperDARN radar and ground magnetometer observations. The model field aligned current is compared with field aligned currents derived from the FAST energetic particle spectra and magnetic field measurements. In all four events downward currents appear to be carried, partially by upgoing electrons below the FAST energy detection threshold (5 eV), but also consist of a mixture of hotter downgoing magnetospheric electrons and upgoing ionospheric electrons of energies 30 eV -- 1 keV. In two of the events downgoing magnetospheric electrons with energies of a few keV, which are associated with upward field aligned currents of ~ 1 microA m --2, are observed. Strong intervals of upward current show that small-scale structuring of ~50 km has been imposed on the current carriers, which is thought to be associated with a mode conversion of an ideal magnetohydrodynamic (MHD) Alfven wave to an inertial Alfven wave.
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Eltrass, Ahmed Said Hassan Ahmed. "The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51804.
Full textAbstract:
The mid-latitude ionosphere is more complicated than previously thought, as it includes many different scales of wave-like structures. Recent studies reveal that the mid-latitude ionospheric irregularities are less understood due to lack of models and observations that can explain the characteristics of the observed wave structures. Since temperature and density gradients are a persistent feature in the mid-latitude ionosphere near the plasmapause, the drift mode growth rate at short wavelengths may explain the mid-latitude decameter-scale ionospheric irregularities observed by the Super Dual Auroral Radar Network (SuperDARN). In the context of this dissertation, we focus on investigating the plasma waves responsible for the mid-latitude ionospheric irregularities and studying their influence on Global Positioning System (GPS) scintillations.
First, the physical mechanism of the Temperature Gradient Instability (TGI), which is a strong candidate for producing mid-latitude irregularities, is proposed. The electro- static dispersion relation for TGI is extended into the kinetic regime appropriate for High- Frequency (HF) radars by including Landau damping, finite gyro-radius effects, and tem- perature anisotropy. The kinetic dispersion relation of the Gradient Drift Instability (GDI) including finite ion gyro-radius effects is also solved to consider decameter-scale waves gen- eration. The TGI and GDI calculations are obtained over a broad set of parameter regimes to underscore limitations in fluid theory for short wavelengths and to provide perspective on the experimental observations.
Joint measurements by the Millstone Hill Incoherent Scatter Radar (ISR) and the Su- perDARN HF radar located at Wallops Island, Virginia have identified the presence of decameter-scale electron density irregularities that have been proposed to be responsible for low-velocity Sub-Auroral Ionospheric Scatter (SAIS) observed by SuperDARN radars. In order to investigate the mechanism responsible for the growth of these irregularities, a time series for the growth rate of both TGI and GDI is developed. The time series is computed for both perpendicular and meridional density and temperature gradients. The growth rate comparison shows that the TGI is the most likely generation mechanism for the observed quiet-time irregularities and the GDI is expected to play a relatively minor role in irregular- ity generation. This is the first experimental confirmation that mid-latitude decameter-scale ionospheric irregularities are produced by the TGI or by turbulent cascade from primary irregularity structures produced from this instability. The quiet- and disturbed-times plasma wave irregularities are compared by investigating co-located experimental observations by the Blackstone SuperDARN radar and the Millstone Hill ISR under various sets of geomagnetic conditions. The radar observations in conjunction with growth rate calculations suggest that the TGI in association with the GDI or a cascade product from them may cause the observations of disturbed-time sub-auroral ionospheric irregularities.
Following this, the nonlinear evolution of the TGI is investigated utilizing gyro-kinetic Particle-In-Cell (PIC) simulation techniques with Monte Carlo collisions for the first time. The purpose of this investigation is to identify the mechanism responsible for the nonlinear saturation as well as the associated anomalous transport. The simulation results indicate that the nonlinear E x B convection (trapping) of the electrons is the dominant TGI sat- uration mechanism. The spatial power spectra of the electrostatic potential and density fluctuations associated with the TGI are also computed and the results show wave cascad- ing of TGI from kilometer scales into the decameter-scale regime of the radar observations. This suggests that the observed mid-latitude decameter-scale ionospheric irregularities may be produced directly by the TGI or by turbulent cascade from primary longer-wavelength irregularity structures produced from this instability.
Finally, the potential impact of the mid-latitude ionospheric irregularities on GPS signals is investigated utilizing modeling and observations. The recorded GPS data at mid-latitude stations are analyzed to study the amplitude and phase fluctuations of the GPS signals and to investigate the spectral index variations due to ionospheric irregularities. The GPS measurements show weak to moderate scintillations of GPS L1 signals in the presence of ionospheric irregularities during disturbed geomagnetic conditions. The GPS spectral indices are calculated and found to be in the same range of the numerical simulations of TGI and GDI. Both simulation results and GPS spectral analysis are consistent with previous in-situ satellite measurements during disturbed periods, showing that the spectral index of mid- latitude density irregularities are of the order 2. The scintillation results along with radar observations suggest that the observed decameter-scale irregularities that cause SuperDARN backscatter, co-exist with kilometer-scale irregularities that cause L-band scintillations. The alignment between the experimental, theoretical, and computational results of this study suggests that turbulent cascade processes of TGI and GDI may cause the observations of GPS scintillations that occur under disturbed conditions of the mid-latitude F-region ionosphere. The TGI and GDI wave cascading lends further support to the belief that the E-region may be responsible for shorting out the F-region TGI and GDI electric fields before and around sunset and ultimately leading to irregularity suppression.Ph. D.
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Gong, Yun. "Incoherent Scatter Study of Dynamics in the Ionosphere E- and F-Region at Arecibo." Miami University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=miami1335235946.
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Khotyaintsev, Yuri. "Alfvén Waves and Energy Transformation in Space Plasmas." Doctoral thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3264.
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This thesis is focused on the role of Alfvén waves in the energy transformation and transport in the magnetosphere. Different aspects of Alfvén wave generation, propagation and dissipation are considered. The study involves analysis of experimental data from the Freja, Polar and Cluster spacecraft, as well as theoretical development. An overview of the linear theory of Alfvén waves is presented, including the effects of fnite parallel electron inertia and fnite ion gyroradius, and nonlinear theory is developed for large amplitude Alfvén solitons and structures. The methodology is presented for experimental identification of dispersive Alfvén waves in a frame moving with respect to the plasma, which facilitates the resolution of the space-time ambiguity in such measurements. Dispersive Alfvén waves are identified on field lines from the topside ionosphere up to the magnetopause and it is suggested they play an important role in magnetospheric physics. One of the processes where Alfvén waves are important is the establishment of the field aligned current system, which transports the energy from the reconnection regions at the magnetopause to the ionosphere, where a part of the energy is dissipated. The main mechanism for the dissipation in the top-side ionosphere is related to wave-particle interactions leading to particle energization/heating. An observed signature of such a process is the presence of parallel energetic electron bursts associated with dispersive Alfvén waves. The accelerated electrons (electron beams) are unstable with respect to the generation of high frequency plasma wave modes. Therefore this thesis also demonstrates an indirect coupling between low frequency Alfvén wave and high frequency oscillations.
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Nakanishi, Kunihito. "A study on magnetic fluctuations over the ionospheric E-region driven by the lower atmospheric phenomena." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215320.
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