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1
Chapagain, Narayan P. "Dynamics of Equatorial Spread F Using Ground-Based Optical and Radar Measurements." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/897.
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The Earth's equatorial ionosphere most often shows the occurrence of large plasma density and velocity fluctuations with a broad range of scale sizes and amplitudes. These night time ionospheric irregularities in the F-region are commonly referred to as equatorial spread F (ESF) or plasma bubbles (EPBs). This dissertation focuses on analysis of ground-based optical and radar measurements to investigate the development and dynamics of ESF, which can significantly disrupt radio communication and GPS navigation systems. OI (630.0 nm) airglow image data were obtained by the Utah State University all-sky CCD camera, primarily during the equinox period, from three different longitudinal sectors under similar solar flux conditions: Christmas Island in the Central Pacific Ocean, Ascension Island in South Atlantic, and Brasilia and Cariri in Brazil. Well-defined magnetic field-aligned depletions were observed from each of these sites enabling detailed measurements of their morphology and dynamics. These data have also been used to investigate day-to-day and longitudinal variations in the evolution and distribution of the plasma bubbles, and their nocturnal zonal drift velocities. In particular, comparative optical measurements at different longitudinal sectors illustrated interesting findings. During the post midnight period, the data from Christmas Island consistently showed nearly constant eastward bubble velocity at a much higher value (~80 m/s) than expected, while data from Ascension Island exhibited a most unusual shear motion of the bubble structure, up to 55 m/s, on one occasion with westward drift at low latitude and eastward at higher latitudes, evident within the field of view of the camera.
In addition, long-term radar observations during 1996-2006 from Jicamarca, Peru have been used to study the climatology of post-sunset ESF irregularities. Results showed that the spread F onset times did not change much with solar flux and that their onset heights increased linearly from solar minimum to solar maximum. On average, radar plume onset occurred earlier with increasing solar flux, and plume onset and peak altitudes increased with solar activity. The F-region upward drift velocities that precede spread F onset increased from solar minimum to solar maximum, and were approximately proportional to the maximum prereversal drift peak velocities.
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Mohd, Ali Aiffah. "GNSS in aviation : ionospheric threats at low latitudes." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761026.
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Radio signals propagating through the ionised upper atmosphere (the ionosphere) in low latitude regions of the world can experience amplitude scintillation. This could threaten safety-critical applications of satellite navigation such as aviation. The research presented here studied the effects of amplitude scintillation on a Septentrio PolaRxS geodetic receiver and a Garmin 480 aviation receiver by means of a Spirent GNSS constellation simulator. Different types of fade profiles showed that an abrupt drop in signal strength caused a loss of lock on the signal more often than a profile with a slow, gradual fade. A performance comparison of the two receivers demonstrated that the aviation receiver was more vulnerable than the geodetic receiver. An unexpected loss of lock at a specific fade duration and depth was seen with the Garmin receiver and was not explained. A single fade with a long fade duration was more likely to cause a loss of signal lock compared to rapid multiple fades. Scintillation on signals from low elevation satellites can significantly degrade the precision and integrity of the navigation solution in an aviation receiver; especially if the satellites are within the best geometrical set. RAIM was observed to be no longer available during the critical landing approach phase of the scenario, in the case when all satellites in view were affected by the scintillation-induced signal perturbations. A technique was also developed to simulate L5 scintillation based on real scintillation events of L1, in the absence of real captured data for L5. This was done to enable future investigations on aviation receiver performance when both L1 and L5 frequencies experience scintillation. Analysis indicated that L5 signal can be more vulnerable to the scintillation compared to the L1 signal, which may have important implications for aviation safety.
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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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Khadka, Sovit M. "Multi-diagnostic Investigations of the Equatorial and Low-latitude Ionospheric Electrodynamics and Their Impacts on Space-based Technologies." Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:108001.
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Thesis advisor: Prof. Michael J. NaughtonThesis advisor: Dr. Cesar E. Valladares
The equatorial and low-latitude ionosphere of the Earth exhibits unique features on its structuring, coupling, and electrodynamics that offer the possibility to forecast the dynamics and fluctuations of ionospheric plasma densities at later times. The scientific understanding and forecasting of ionospheric plasma are necessary for several practical applications, such as for mitigating the adverse effects of space weather on communication, navigation, power grids, space mission, and for various scientific experiments and applications. The daytime equatorial electrojet (EEJ), equatorial ionization anomaly (EIA), as well as nighttime equatorial plasma bubble (EPB) and plasma blobs are the most prominent low-latitude ionospheric phenomena. This dissertation focuses on the multi-diagnostic study of the mechanism, properties, abnormalities, and interrelationships of these phenomena to provide significant contributions to space weather communities from the ground- and space-based measurements. A strong longitudinal, seasonal, day-to-day variability and dependency between EEJ, ExB vertical plasma drift, and total electron content (TEC) in the EIA distribution are seen in the equatorial and low-latitude region. In general, the EEJ strength is stronger in the west coast of South America than in its east coast. The variability of the EEJ in the dayside ionosphere significantly affects the ionospheric electron density variation, dynamics of the peak height of F2-layer, and TEC distributions as the EEJ influences the vertical transport mechanism of the ionospheric plasma. The eastward electric field (EEF) and the neutral wind play a decisive role in controlling the actual configuration of the EIA. The trans-equatorial neutral wind profile calculated using data from the Second-generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator and a physics-based numerical model, LLIONS (Low-Latitude IONospheric Sector) give new perspectives on the effects of daytime meridional neutral winds on the consequent evolution of the asymmetry of the equatorial TEC anomalies during the afternoon onwards. The spatial configurations including the strength, shape, amplitude and latitudinal extension of the EIA crests are affected by the EEF associated with the EEJ under undisturbed conditions, whereas the meridional neutral winds play a significant role in the development of their asymmetric structure in the low-latitude ionosphere. Additionally, the SWARM satellite constellation and the ground-based LISN (Low-Latitude Ionospheric Sensor Network) data allow us to resolve the space-time ambiguity of past single-satellite studies and detect the drastic changes that EPBs and plasma blobs undergo on a short time scale. The coordinated quantitative analysis of a plasma density observation shows evidence of the association of plasma blobs with EPBs via an appropriate geomagnetic flux tube. Plasma blobs were initially associated with the EPBs and remained at the equatorial latitude right above the EPBs height, but later were pushed away from geomagnetic equator towards EIA latitudes by the EPB/ depleted flux tubes that grew in volume. Further, there exists a strong correlation between the noontime equatorial electrojet and the GPS-derived TEC distributions during the afternoon time period, caused by vertical E × B drift via the fountain effect. Nevertheless, only a minor correlation likely exists between the peak EEJ and the net postsunset ionospheric scintillation index (S4) greater than 0.2. This study not only searches for a mutual relationship between the midday, afternoon and nighttime ionospheric phenomena but also aims at providing a possible route to improve our space weather forecasting capability by predicting nighttime ionospheric irregularities based on midday measurements at the equatorial and low latitudes
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
5
Orford, Nicola Diane. "Behaviour of quiet time ionospheric disturbances at African equatorial and midlatitude regions." Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/62672.
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Extreme ionospheric and geomagnetic disturbances affect technology adversely. Prestorm enhancements, considered a potential predictor of geomagnetic storms, occur during quiet conditions prior to geomagnetic disturbances. The ionosphere experiences general disturbances during quiet geomagnetic conditions and these Q- disturbances remain unexplored over Africa. This study used TEC data to characterize the morphology of Q-disturbances over Africa, exploring variations with solar cycle, season, time of occurrence and latitude. Observations from 10 African GPS stations in the equatorial and midlatitude regions show that Q-disturbances in the equatorial region are predominantly driven by E x B variations, while multiple mechanisms affect the midlatitude region. Q- disturbances occur more frequently during nighttime than during daytime and no seasonal trend is observed. Midlatitude Q-disturbance mechanisms are explored in depth, considering substorm activity, the plasmaspheric contribution to GPS TEC and plasma transfer between conjugate points. Substorm activity is not a dominant mechanism, although Q-disturbances occurring under elevated substorm conditions tend to have longer duration and larger amplitude than general Q-disturbances. Many observed Q-disturbances become non-significant once the plasmaspheric contribution to the TEC measurements is removed, indicating that these disturbances occur within the plasmasphere, and not the ionosphere. Transfer of plasma between conjugate points does not seem to be a mechanism driving Q-disturbances, as the corresponding nighttime behaviour expected between depletions in the summer hemisphere and enhancements in the winter hemisphere is not observed. Pre-storm enhancements occur infrequently, rendering them a poor predictor of geomagnetic disturbances. Pre-storm enhancement morphology does not differ significantly from general quiet time enhancement morphology, suggesting pre-storms are not a special case of Q-disturbances.
6
李若愚 and Yeuk-Yue Tony Li. "The equatorial ionospheric anomaly in East Asia from solar minimun to solar maximum." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1993. http://hub.hku.hk/bib/B31211677.
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Li, Yeuk-Yue Tony. "The equatorial ionospheric anomaly in East Asia from solar minimum to solar maximum /." [Hong Kong : University of Hong Kong], 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13597577.
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Matamba, Tshimangadzo Merline. "Long-term analysis of ionospheric response during geomagnetic storms in mid, low and equatorial latitudes." Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/63991.
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Understanding changes in the ionosphere is important for High Frequency (HF) communications and navigation systems. Ionospheric storms are the disturbances in the Earth’s upper atmosphere due to solar activities such as Coronal Mass Ejections (CMEs), Corotating interaction Regions (CIRs) and solar flares. This thesis reports for the first time on an investigation of ionospheric response to great geomagnetic storms (Disturbance storm time, Dst ≤ −350 nT) that occurred during solar cycle 23. The storm periods analysed were 29 March - 02 April 2001, 27 - 31 October 2003, 18 - 23 November 2003 and 06 - 11 November 2004. Global Navigation Satellite System (GNSS), Total Electron Content (TEC) and ionosonde critical frequency of F2 layer (foF2) data over northern hemisphere (European sector) and southern hemisphere (African sector) mid-latitudes were used to study the ionospheric responses within 15E° - 40°E longitude and ±31°- ±46° geomagnetic latitude. Mid-latitude regions within the same longitude sector in both hemispheres were selected in order to assess the contribution of the low latitude changes especially the expansion of Equatorial Ionization Anomaly (EIA) also known as the dayside ionospheric super-fountain effect during these storms. In all storm periods, both negative and positive ionospheric responses were observed in both hemispheres. Negative ionospheric responses were mainly due to changes in neutral composition, while the expansion of the EIA led to pronounced positive ionospheric storm effect at mid-latitudes for some storm periods. In other cases (e.g 29 October 2003), Prompt Penetration Electric Fields (PPEF), EIA expansion and large scale Traveling Ionospheric Disturbances (TIDs) were found to be present during the positive storm effect at mid-latitudes in both hemispheres. An increase in TEC on the 28 October 2003 was because of the large solar flare with previously determined intensity of X45± 5. A further report on statistical analysis of ionospheric storm effects due to Corotating Interaction Region (CIR)- and Coronal Mass Ejection (CME)-driven storms was performed. The storm periods analyzed occurred during the period 2001 - 2015 which covers part of solar cycles 23 and 24. Dst≤ -30 nT and Kp≥ 3 indices were used to identify the storm periods considered. Ionospheric TEC derived from IGS stations that lie within 30°E - 40°E geographic longitude in mid, low and equatorial latitude over the African sector were used. The statistical analysis of ionospheric storm effects were compared over mid, low and equatorial latitudes in the African sector for the first time. Positive ionospheric storm effects were more prevalent during CME-driven and CIR-driven over all stations considered in this study. Negative ionospheric storm effects occurred only during CME-driven storms over mid-latitude stations and were more prevalent in summer. The other interesting finding is that for the stations considered over mid-, low, and equatorial latitudes, negative-positive ionospheric responses were only observed over low and equatorial latitudes. A significant number of cases where the electron density changes remained within the background variability during storm conditions were observed over the low latitude stations compared to other latitude regions.
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Xu, Dongyang. "BEIDOU AND GPS DUAL CONSTELLATION VECTOR TRACKING DURING IONOSPHERE SCINTILLATION AT EQUATORIAL REGION." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1407512226.
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Galmiche, Aurélien. "Modélisation de la scintillation ionosphérique en zone équatoriale : application à l'inversion des signaux GNSS pour la caractérisation de la turbulence." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30053.
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L'ionosphère est un milieu ionisé dont les variations spatiales et temporelles de densité électronique perturbent la propagation des ondes électromagnétiques. En particulier, la nature turbulente du plasma ionosphérique conduit à des fluctuations rapides de l'amplitude et de la phase des signaux radioélectriques : c'est le phénomène de scintillation ionosphérique dont les effets sont particulièrement sensibles aux latitudes équatoriales sur les systèmes ayant un besoin accru de précision, de disponibilité et d'intégrité de la mesure, tel que les systèmes de localisation GNSS. L'objectif de cette thèse est justement d'exploiter de façon opportune les effets de la scintillation ionosphérique sur le signal pour proposer un sondage des caractéristiques de l'ionosphère turbulente par inversion des mesures GNSS. Dans un premier temps, les spécificités de la dynamique du plasma ionosphérique équatorial responsable des effets de scintillation sont rappelées. Ensuite, à partir d'une description spectrale des fluctuations turbulentes de densité électronique, une modélisation analytique puis numérique de la propagation transionosphérique sont proposées. Celles-ci sont complétées par la prise en compte du récepteur GNSS, finalisant la modélisation du problème direct. À ce stade, un algorithme d'inversion original des données GNSS est proposé. Son application intensive à la base de données SAGAIE collectée en Afrique équatoriale démontre alors la capacité de l'approche inverse à restituer divers paramètres descriptifs de la turbulence ionosphériqueThe ionosphere is an ionized medium, into which the spatio-temporal electronic density variations disrupt the electromagnetic waves propagation. The turbulent ionospheric plasma is in particular linked to rapid amplitude and phase fluctuations of the radio electric signals: this is the ionospheric scintillation phenomenon. Especially around the equatorial latitudes, systems needing great accuracy, availability and measurement integrity are particularly sensitive to its effects. This is the case of the positioning systems using the GNSS technology. The aim of this thesis is to exploit insightly the ionospheric scintillation effects on the signal in order to propose a turbulent ionosphere's characteristics sounding through GNSS measurements inversion. At first, the specificities of the ionosphere's plasma dynamics accounting for the scintillation effects are reminded. Then, from a spectral description of the electronic density's turbulent fluctuations, an analytic and a numeric model of the transionospheric propagation are introduced. They are completed by considering the GNSS receiver. This step finalizes the direct problem's modelization. A new GNSS data inversion algorithm is then come up with. Its intensive application to the SAGAIE database (collected in equatorial Africa) shows the invers approach's capacity to return various parameters describing the ionospheric turbulences
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Joshi, Dev Raj. "Artificial and Natural Disturbances in the Equatorial Ionosphere: Results from the MOSC Experiment and the C/NOFS satellite mission." Thesis, Boston College, 2019. http://hdl.handle.net/2345/bc-ir:108706.
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Thesis advisor: Michael J. NaughtonThesis advisor: Keith M. Groves
The low-latitude ionosphere is characterized by large-scale instabilities in the post-sunset hours due to the distinct geometry of the earth’s magnetic field lines at the equator. The magnetic field lines are horizontal at the equator contributing to the high vertical drift velocity of the plasma bubbles growing from the bottomside of the ionospheric F-region. The phenomenon, commonly known as equatorial spread F, is an important problem in aeronomy as it can cause radio wave scintillation effects representing the most critical impacts of space weather on man-made technologies, such as satellite communications and global navigation satellite systems (GNSS). Here, we present results from an artificial ionospheric modification experiment as well as from naturally occurring instabilities in the equatorial ionosphere. An artificial plasma cloud was created in the bottomside of the ionospheric F-layer during the Metal Oxide Space Cloud (MOSC) experiment in May 2013 to study the interactions of artificial ionization with the background plasma under the hypothesis that the artificial plasma might suppress the occurrence of natural instabilities. While the suppression hypothesis remains open to debate, the propagation results confirm that the injection of artificial ionization in the lower F–region causes dramatic changes to the ambient HF propagation environment. We also calculate various parameters needed to evaluate the growth rate of Rayleigh- Taylor instability created in the F-region bottomside of the ionosphere from the thirteen days of High-Frequency (HF) radar data during the MOSC campaign. These parameters have been used to calculate the growth rate to predict the diurnal variability of the spread F occurrence. The growth rate has also been calculated from model ionospheric profiles optimized by ray-tracing techniques to match actual delays as observed in the oblique HF links. The calculated growth rate provides a close prediction of spread F development as seen in its correlation with the ground scintillation observations. With regard to natural processes, data from the Air Force Research Laboratory (AFRL) / the National Aeronautics and Space Administration (NASA) Communications/Navigations Outage Forecasting System (C/NOFS) satellite mission has been analyzed to investigate the characteristics of equatorial ionospheric irregularities from in situ observations. We present a comprehensive investigation on the variation of apex-altitude distribution of equatorial ionospheric irregularities with solar activity supported by modeling, simulation and comparisons with ground- and space-based in situ density observations. We also analyze Physics Based Model (PBMOD) ionospheric model results to determine if a physics-based model can reproduce the observed dependence of bubble height on solar activity
Thesis (PhD) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Giday, Nigussie Mezgebe. "Tomographic imaging of East African equatorial ionosphere and study of equatorial plasma bubbles." Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/63980.
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In spite of the fact that the African ionospheric equatorial region has the largest ground footprint along the geomagnetic equator, it has not been well studied due to the absence of adequate ground-based instruments. This thesis presents research on both tomographic imaging of the African equatorial ionosphere and the study of the ionospheric irregularities/equatorial plasma bubbles (EPBs) under varying geomagnetic conditions. The Multi-Instrument Data Analysis System (MIDAS), an inversion algorithm, was investigated for its validity and ability as a tool to reconstruct multi-scaled ionospheric structures for different geomagnetic conditions. This was done for the narrow East African longitude sector with data from the available ground Global Positioning Sys-tem (GPS) receivers. The MIDAS results were compared to the results of two models, namely the IRI and GIM. MIDAS results compared more favourably with the observation vertical total electron content (VTEC), with a computed maximum correlation coefficient (r) of 0.99 and minimum root-mean-square error (RMSE) of 2.91 TECU, than did the results of the IRI-2012 and GIM models with maximum r of 0.93 and 0.99, and minimum RMSE of 13.03 TECU and 6.52 TECU, respectively, over all the test stations and validation days. The ability of MIDAS to reconstruct storm-time TEC was also compared with the results produced by the use of a Artificial Neural Net-work (ANN) for the African low- and mid-latitude regions. In terms of latitude, on average,MIDAS performed 13.44 % better than ANN in the African mid-latitudes, while MIDAS under performed in low-latitudes. This thesis also reports on the effects of moderate geomagnetic conditions on the evolution of EPBs and/or ionospheric irregularities during their season of occurrence using data from (or measurements by) space- and ground-based instruments for the east African equatorial sector. The study showed that the strength of daytime equatorial electrojet (EEJ), the steepness of the TEC peak-to-trough gradient and/or the meridional/transequatorial thermospheric winds sometimes have collective/interwoven effects, while at other times one mechanism dominates. In summary, this research offered tomographic results that outperform the results of the commonly used (“standard”) global models (i.e. IRI and GIM) for a longitude sector of importance to space weather, which has not been adequately studied due to a lack of sufficient instrumentation.
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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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SILVA, Leide Pricila da. "Observação de oscilações de 3-4 dias na mesosfera-ionosfera equatorial." Universidade Federal de Campina Grande, 2015. http://dspace.sti.ufcg.edu.br:8080/jspui/handle/riufcg/2004.
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Capes
Foi investigado o acoplamento vertical em baixas latitudes no sistema atmosfera ionosfera na região MLT equatorial impulsionado pela onda de 3-4 dias. Neste trabalho, se identifi cou eventos da onda 3-4 dias durante o per odo de janeiro a dezembro de 2005 nos ventos neutros obtidos por medições de radar localizados em São João do Cariri-PB, Brasil. A variação de 3-4 dias nas correntes elétricas ionosféricas na região E registrado por perturbações no campo geomagnético, foi estudada através de 4 magnetômetros localizados na região equatorial. Os resultados mostraram que as oscilações ocorridas nos ventos zonais em fevereiro-março, maio-junho, agosto e outubro-novembro, são compatíveis com a propagação de ondas ultra-rápido Kelvin. A estrutura de fase vertical foi descendente, compatível com a energia da onda ascendente, e comprimentos de onda verticais de cerca de 45 km foram encontrados nos primeiro, segundo e quarto eventos, o terceiro evento apresenta comprimento de onda vertical de 62 km. Os resultados mostraram eventos quase simultâneos da onda de 3-4 dias no campo geomagnético e nos ventos MLT, cuja propagação é para leste, que pode ser interpretado como devido à onda ultra-rápida de Kelvin, exceto para o terceiro acontecimento que mostrou propagação para oeste. O parâmetro que parece ser afetado é o dínamo campo elétrico.
Vertical coupling in the low latitude atmosphere-ionosphere system driven by the 3-4 day wave in the equatorial MLT region was investigated. In this work a 3-4 day wave event during the period from January to December of 2005 identi ed in the neutral winds by radar measurements located at São João do Cariri-PB, Brazil. The 3-4 day variation in the ionospheric electric currents in the E region registered by perturbations in the geomagnetic eld, was detected in the data from 4 magnetometer located in the equatorial region. The results showed that only the oscillations that occurred in the zonal winds in February-March, May-June, August, and October-November, are compatible with the ultra-fast Kelvin wave propagation. The vertical phase structure was descendent, compatible with ascending wave energy, and vertical wavelengths of about 45 km were found for in the rst, second and fourth events, the third event 62 km. The results showed quasi-simultaneous 3-4 day oscillation in the geomagnetic eld and in the MLT winds, in which the of propagation is eastward, it can be interpreted as due to ultra-fast Kelvin wave, except for the third event that showed westward propagation. The parameter that appears to be a a ected is the dynamo electric eld.
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Hui, Debrup. "Altitudinal Variability of Quiet-time Plasma Drifts in the Equatorial Ionosphere." DigitalCommons@USU, 2015. https://digitalcommons.usu.edu/etd/4536.
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The plasma drifts or electric fields and their structures in the ionosphere affect the accuracy of the present-day space-based systems. For the first time, we have used ionospheric plasma drift data from Jicamarca radar measurements to study the climatology of altitudinal variations of vertical and zonal plasma drifts in low latitudes during daytime. We used data from 1998 to 2014 to derive these climatological values in bimonthly bins from 150 km to 600 km. For the vertical plasma drifts, we observed the drifts increasing with altitudes in the morning and slowly changing to drifts decreasing with altitude in the afternoon hours. The drifts change mostly linearly from E- to F-region altitudes except in the morning hours of May-June when the gradients are very small. The zonal drifts show a highly nonlinear increase in the westward drifts at the lower altitudes and then increase slowly at the higher altitudes. We see a break in the slopes at lower altitudes during the morning hours of March-April and May-June. The E-region zonal drifts, unlike vertical drifts, show a very large variability compared to F-region drifts. We also explored the altitudinal profiles of vertical drifts during late afternoon and evening hours when the electrodynamic properties in the ionosphere change rapidly. For the first time using drifts up to 2000 km, we have shown the drifts increase and decrease below and above the F-region peak before becoming height independent. These structures arise to satisfy the curl-free condition of electric fields in low latitudes. The altitudinal gradients of vertical drifts are balanced by a time derivative of the zonal drifts to satisfy the curl-free condition of electric fields. We have shown how these structures evolve with local time around the dusk sector and change with solar flux. During solar minimum, the peak region can go well below 200 km. The present-day electric field models do not incorporate these gradients, particularly in the evening sectors when they change very rapidly. Very often their results do not match with the observations. Including these gradients along with proper magnetic field models will improve the model results and accuracy of our navigation, communication, and positioning systems.
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McKinstry, John W. "A comparison of trans-equatorial ionosphere propagation predictions from AMBCOM with measured data." Thesis, Monterey, California. Naval Postgraduate School, 1993. http://hdl.handle.net/10945/26933.
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This thesis examines radio propagation conditions over trans- equatorial (TE) paths. The study precedes Project PENEX, a field experiment to measure and collect calibrated HF skywave signal strength data for polar, equatorial. and near-vertical incidence propagation paths. PENEX will benchmark the absolute accuracy of the signal-to-noise models in the MEDUSA propagation model now being developed by the Naval Command, Control and Ocean Surveillance Center. Since only minimal information is available about TE paths, a comprehensive review of the published literature on TE experiments was completed, with emphasis oil TE paths between magnetic conjugate points. Data from such paths have revealed the presence of unusual propagation i-nodes which are not predicted by standard propagation programs such as PROPHET, IONCAP, and AMBCOM. The review of the literature revealed that Stanford Research Institute (SRI) published measured data on a TE path between the Pacific islands of Kauai and Rarotonga. A comparison was made between the SRI data and predictions for the same path to assess the usefulness of current prediction programs for TE paths. The SRI AMBCOM program was used for this comparison. As expected, sizeable differences were found between the predicted and measured results, especially during times when unusual propagation modes were present. This suggests that prediction programs should be modified to include the observed TE modes..
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Cesaroni, Claudio <1980>. "A multi-instrumental approach to the study of equatorial ionosphere over South America." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6889/1/Cesaroni_Claudio_tesi.pdf.
Full textAbstract:
An extensive study of the morphology and the dynamics of the equatorial ionosphere over South America is presented here. A multi parametric approach is used to describe the physical characteristics of the ionosphere in the regions where the combination of the thermospheric electric field and the horizontal geomagnetic field creates the so-called Equatorial Ionization Anomalies. Ground based measurements from GNSS receivers are used to link the Total Electron Content (TEC), its spatial gradients and the phenomenon known as scintillation that can lead to a GNSS signal degradation or even to a GNSS signal ‘loss of lock’. A new algorithm to highlight the features characterizing the TEC distribution is developed in the framework of this thesis and the results obtained are validated and used to improve the performance of a GNSS positioning technique (long baseline RTK). In addition, the correlation between scintillation and dynamics of the ionospheric irregularities is investigated. By means of a software, here implemented, the velocity of the ionospheric irregularities is evaluated using high sampling rate GNSS measurements. The results highlight the parallel behaviour of the amplitude scintillation index (S4) occurrence and the zonal velocity of the ionospheric irregularities at least during severe scintillations conditions (post-sunset hours). This suggests that scintillations are driven by TEC gradients as well as by the dynamics of the ionospheric plasma. Finally, given the importance of such studies for technological applications (e.g. GNSS high-precision applications), a validation of the NeQuick model (i.e. the model used in the new GALILEO satellites for TEC modelling) is performed. The NeQuick performance dramatically improves when data from HF radar sounding (ionograms) are ingested. A custom designed algorithm, based on the image recognition technique, is developed to properly select the ingested data, leading to further improvement of the NeQuick performance.
18
Cesaroni, Claudio <1980>. "A multi-instrumental approach to the study of equatorial ionosphere over South America." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6889/.
Full textAbstract:
An extensive study of the morphology and the dynamics of the equatorial ionosphere over South America is presented here. A multi parametric approach is used to describe the physical characteristics of the ionosphere in the regions where the combination of the thermospheric electric field and the horizontal geomagnetic field creates the so-called Equatorial Ionization Anomalies. Ground based measurements from GNSS receivers are used to link the Total Electron Content (TEC), its spatial gradients and the phenomenon known as scintillation that can lead to a GNSS signal degradation or even to a GNSS signal ‘loss of lock’. A new algorithm to highlight the features characterizing the TEC distribution is developed in the framework of this thesis and the results obtained are validated and used to improve the performance of a GNSS positioning technique (long baseline RTK). In addition, the correlation between scintillation and dynamics of the ionospheric irregularities is investigated. By means of a software, here implemented, the velocity of the ionospheric irregularities is evaluated using high sampling rate GNSS measurements. The results highlight the parallel behaviour of the amplitude scintillation index (S4) occurrence and the zonal velocity of the ionospheric irregularities at least during severe scintillations conditions (post-sunset hours). This suggests that scintillations are driven by TEC gradients as well as by the dynamics of the ionospheric plasma. Finally, given the importance of such studies for technological applications (e.g. GNSS high-precision applications), a validation of the NeQuick model (i.e. the model used in the new GALILEO satellites for TEC modelling) is performed. The NeQuick performance dramatically improves when data from HF radar sounding (ionograms) are ingested. A custom designed algorithm, based on the image recognition technique, is developed to properly select the ingested data, leading to further improvement of the NeQuick performance.
19
wang, xiaoni. "A STUDY OF EQUATORIAL IONOPSHERIC VARIABILITY USING SIGNAL PROCESSING TECHNIQUES." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2415.
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The dependence of equatorial ionosphere on solar irradiances and geomagnetic activity are studied in this dissertation using signal processing techniques. The statistical time series, digital signal processing and wavelet methods are applied to study the ionospheric variations. The ionospheric data used are the Total Electron Content (TEC) and the critical frequency of the F2 layer (foF2). Solar irradiance data are from recent satellites, the Student Nitric Oxide Explorer (SNOE) satellite and the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite. The Disturbance Storm-Time (Dst) index is used as a proxy of geomagnetic activity in the equatorial region. The results are summarized as follows. (1) In the short-term variations < 27-days, the previous three days solar irradiances have significant correlation with the present day ionospheric data using TEC, which may contribute 18% of the total variations in the TEC. The 3-day delay between solar irradiances and TEC suggests the effects of neutral densities on the ionosphere. The correlations between solar irradiances and TEC are significantly higher than those using the F10.7 flux, a conventional proxy for short wavelength band of solar irradiances. (2) For variations < 27 days, solar soft X-rays show similar or higher correlations with the ionosphere electron densities than the Extreme Ultraviolet (EUV). The correlations between solar irradiances and foF2 decrease from morning (0.5) to the afternoon (0.1). (3) Geomagnetic activity plays an important role in the ionosphere in short-term variations < 10 days. The average correlation between TEC and Dst is 0.4 at 2-3, 3-5, 5-9 and 9-11 day scales, which is higher than those between foF2 and Dst. The correlations between TEC and Dst increase from morning to afternoon. The moderate/quiet geomagnetic activity plays a distinct role in these short-term variations of the ionosphere (~0.3 correlation).Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering PhD
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Dal, Poz William Rodrigo. "Posicionamento relativo na região equatorial em diversas condições ionosféricas /." Presidente Prudente : [s.n.], 2005. http://hdl.handle.net/11449/88532.
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Orientador: Paulo de Oliveira CamargoResumo: Assim como no posicionamento por ponto, os resultados obtidos no posicionamento relativo a partir de receptores de uma freqüência são afetados pelo efeito sistemático da ionosfera, que atualmente é uma das maiores fontes de erro no posicionamento com GPS. O problema principal no posicionamento relativo é devido ao gradiente espacial do conteúdo total de elétrons (TEC) presente na ionosfera, enquanto que no posicionamento por ponto o principal problema é a magnitude do TEC. Assim, no posicionamento relativo fica mais complicado de se analisar o efeito da ionosfera nos resultados obtidos, principalmente na região equatorial, onde várias irregularidades e anomalias ocorrem. Este projeto analisa o efeito da ionosfera no posicionamento relativo estático na região equatorial, em diversas condições ionosféricas, a partir de uma abordagem teórica e prática. Foram processados dados somente da portadora L1 com a dupla diferença da fase e do código. A análise dos resultados foi realizada a partir das discrepâncias das coordenadas consideradas verdadeiras com as obtidas no processamento das linhas de base. Três experimentos foram realizados, no qual foi possível analisar a influência da ionosfera no posicionamento relativo a partir de vários aspectos. De uma forma geral, verificou-se na prática a complexidade de definir se determinada linha de base é curta ou média, devido ao gradiente espacial do TEC. Também foram verificados efeitos da cintilação ionosférica e de uma tempestade geomagnética nos resultados obtidos.
Abstract: The obtained results in the relative positioning, as well as in the point positioning, are affected by the ionosphere systematic effects, which is one of major error sources in the GPS positioning. The main problem in the relative positioning is due to the Total Electron Content (TEC) variation of the ionosphere, while in the point positioning the main problem is the magnitude of the TEC. Thus, the effects of the ionosphere in the relative positioning are more difficult to analyze, mainly in the equatorial region, where several irregularities and anomalies occur. This research analyzes the ionosphere effect in the relative positioning in the equatorial region considering several ionosphere conditions, both from theoretical and practical standpoints. Only L1 carrier data have been processed using L1 phase and C/A-code doubledifferences. The analyze of the obtained results have been carried out from the discrepancies between the "true" coordinates and corresponding ones obtained in the processing of the baselines. Three experiments have been accomplished, in which it was possible to analyze the ionosphere influence in the relative positioning considering several aspects. In general, due to TEC variations, it has been verified, in practice, the complexity of defining whether a given baseline length is short or medium. It has been also verified in the results the effects of the ionospheric scintillation and of a geomagnetic storm.
Mestre
21
Dal, Poz William Rodrigo [UNESP]. "Posicionamento relativo na região equatorial em diversas condições ionosféricas." Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/88532.
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Assim como no posicionamento por ponto, os resultados obtidos no posicionamento relativo a partir de receptores de uma freqüência são afetados pelo efeito sistemático da ionosfera, que atualmente é uma das maiores fontes de erro no posicionamento com GPS. O problema principal no posicionamento relativo é devido ao gradiente espacial do conteúdo total de elétrons (TEC) presente na ionosfera, enquanto que no posicionamento por ponto o principal problema é a magnitude do TEC. Assim, no posicionamento relativo fica mais complicado de se analisar o efeito da ionosfera nos resultados obtidos, principalmente na região equatorial, onde várias irregularidades e anomalias ocorrem. Este projeto analisa o efeito da ionosfera no posicionamento relativo estático na região equatorial, em diversas condições ionosféricas, a partir de uma abordagem teórica e prática. Foram processados dados somente da portadora L1 com a dupla diferença da fase e do código. A análise dos resultados foi realizada a partir das discrepâncias das coordenadas consideradas verdadeiras com as obtidas no processamento das linhas de base. Três experimentos foram realizados, no qual foi possível analisar a influência da ionosfera no posicionamento relativo a partir de vários aspectos. De uma forma geral, verificou-se na prática a complexidade de definir se determinada linha de base é curta ou média, devido ao gradiente espacial do TEC. Também foram verificados efeitos da cintilação ionosférica e de uma tempestade geomagnética nos resultados obtidos.
The obtained results in the relative positioning, as well as in the point positioning, are affected by the ionosphere systematic effects, which is one of major error sources in the GPS positioning. The main problem in the relative positioning is due to the Total Electron Content (TEC) variation of the ionosphere, while in the point positioning the main problem is the magnitude of the TEC. Thus, the effects of the ionosphere in the relative positioning are more difficult to analyze, mainly in the equatorial region, where several irregularities and anomalies occur. This research analyzes the ionosphere effect in the relative positioning in the equatorial region considering several ionosphere conditions, both from theoretical and practical standpoints. Only L1 carrier data have been processed using L1 phase and C/A-code doubledifferences. The analyze of the obtained results have been carried out from the discrepancies between the true coordinates and corresponding ones obtained in the processing of the baselines. Three experiments have been accomplished, in which it was possible to analyze the ionosphere influence in the relative positioning considering several aspects. In general, due to TEC variations, it has been verified, in practice, the complexity of defining whether a given baseline length is short or medium. It has been also verified in the results the effects of the ionospheric scintillation and of a geomagnetic storm.
22
Salomoni, Christiane da Silva Santos. "GPS e ionosfera: estudo do comportamento do TEC e de sua influência no posicionamento com GPS na região brasileira em períodos de alta e baixa atividade solar." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/15752.
Full textAbstract:
A ionosfera é uma das principais fontes de erro sistemático das observáveis GPS (Global Positioning System - Sistema de Posicionamento Global), pois, por ser um meio dispersivo, ela afeta a propagação de ondas eletromagnéticas, fazendo com que a modulação e a fase das ondas portadoras transmitidas pelos satélites GPS sofram, respectivamente, um retardo e um avanço, o que, por sua vez, provoca um erro na distância medida entre o satélite e o receptor. Esse erro é inversamente proporcional ao quadrado da freqüência do sinal e diretamente proporcional ao TEC (Total Electron Content - Conteúdo Total de Elétrons), ou seja, à densidade de elétrons presentes na ionosfera ao longo do caminho entre o satélite e a antena receptora. O TEC sofre variações regulares, cujo comportamento pode ser verificado ao longo do dia, ao longo das estações do ano e também ao longo de ciclos de aproximadamente onze anos (associados à ocorrência de manchas solares). Além dessas variações, eventos solares extremos (explosões solares, ejeções coronais de massa, entre outros) podem causar abruptas e significativas mudanças no comportamento do TEC, exercendo grande influência no posicionamento com GPS, principalmente com receptores de uma freqüência. No Brasil, o fator ionosfera é ainda mais relevante, pois essa região é afetada por fenômenos como a Anomalia Equatorial (AE), a Anomalia Magnética do Atlântico Sul (AMAS) e até mesmo pela ocorrência de irregularidades ionosféricas. Pretendendo aprofundar o entendimento da relação entre a ionosfera e o posicionamento com GPS na região brasileira, essa pesquisa analisou dados de TEC e dados de GPS em períodos de alta e baixa atividade solar, bem como em um período geomagneticamente perturbado. Os resultados demonstraram uma relação direta entre a redução do TEC, no período de baixa atividade solar, e a melhora no posicionamento com GPS. Essa melhora se traduziu, no posicionamento por ponto, por uma redução de 59% no erro planimétrico e 64% no erro altimétrico e, no posicionamento relativo, por uma redução de 65% no erro planimétrico e 63% no erro altimétrico. Já durante o período afetado por uma severa tempestade geomagnética verificou-se um comportamento completamente atípico da ionosfera, piorando muitos os resultados do posicionamento relativo, em horários e locais inesperados.The ionosphere is one of the main sources of systemathic error of the observable GPS (Global Positioning System) because as it is a dispersive environment it affects the propagation of electromagnetics waves making the modulation and the phase of signals transmitted by GPS sattelites go through, respectivelly, delay and advance which will cause an error in the measure of the distance between the sattelite and the receptor. This error is inversely proportional to the square of the frequency of the signal and directly proportional to the TEC (Total Electron Content), what means the density of electrons on the ionosphere between the sattelite and the reception antenna. The TEC goes through regular variances, which behaviour can be verified during the day, throughout seasons and also throughout cycles of approximately eleven years (related to the ocorrence of sunspot). Besides these variances, extreme solar events such as solar flares and coronal mass ejection may cause abrupt and significant changes to TEC behavior, exerting big influence in GPS positioning, mainly to monofrequency receptors. In Brazil, the ionosphere factor is even more relevant because this region is affected by phenomena such as the Equatorial Anomaly (EA), the South Atlantic Magnetic Anomaly (SAMA) and even by the ocorrence of ionospheric irregularities. In order to develop knowledge about the relation between ionosphere and GPS positioning in Brazil, on this research TEC and GPS data were analised in periods of high and low solar activity, as well as in a geomagnetic perturbed period. The results showed direct relation between the decreasing of TEC, in the low solar activity period, and the improving of GPS positioning. This improving has resulted in a reduction of 59% in the planimetric error and 64% in the altimetric error in the point positioning and a reduction of 65% in the planimetric error and 63% in the altimetric error in the relative positioning. During the period affected by a severe geomagnetic storm, a completely atypical behavior was identified in the ionosphere, making the results of the relative positioning much worse in unexpected times and locations.
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Lima, Newton Silva de. "Estudo da propagação de ondas de gravidade na ionosfera equatorial, utilizando observações em Manaus (2,9°s, 60°w)." Universidade Federal do Amazonas, 2009. http://tede.ufam.edu.br/handle/tede/3275.
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This work studies the behavior of gravity waves (GW) in the ionosphere over the city of Manaus (2,9oS, 60oW). For that purpose, ionograms which are specters of frequency in function of the altitude and the secular variation of the height for a set of fixed frequencies (3, 4, 5, 6, 7 8 MHz). The observations were analyzed carried through by a system of called radar ionosonde. This system operates in the radio frequency band between 1and 20 MHz. The studied period comprehends a part of solar cycle 23, that is, since August of 2002 until December of 2006. Additionally, it was also observed that the ionosphere presents strong disturbances during geomagnetically quiet periods. These disturbances are attributed to the propagation of gravity waves which are generated in the lower atmosphere and propagate up to the high atmosphere and ionosphere.
Este trabalho investiga o comportamento de ondas de gravidade (OG) na ionosfera sobre a cidade de Manaus (2,9oS, 60oW). Para tal, foram analisados ionogramas que são espectros de freqüência em função da altitude e a variação temporal da altura, para um conjunto de freqüências fixas (3, 4, 5, 6, 7 8 MHz). As observações foram realizadas por um sistema de radar chamado ionossonda; que pera na faixa de rádio freqüência entre 1 e 20 MHz. O período estudado compreende uma parte do ciclo solar 23, ou seja, desde agosto de 2002 até dezembro de 2006. Observou-se que a ionosfera apresenta fortes perturbações durante períodos geomagneticamente calmos. Estas perturbações são atribuídas a propagação de ondas de gravidade que são geradas na baixa atmosfera e se propagam até a alta atmosfera e ionosfera.
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Chen, Chia-Hung, and 陳佳宏. "Ionospheric Equatorial Ionization Anomaly and Equatorial Electrojet." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/56cpwm.
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碩士國立中央大學
太空科學研究所
94
Many studies show seasonal variations of equatorial ionization anomaly (EIA). In this thesis, the ionospheric total electron content (TEC) in the Asian sector derived from measurements of ground-based receivers of the global positioning system (GPS) is employed to investigate the EIA variations during 1997-2005. In addition, magnetometer data from the Circum-pan Pacific Magnetometer Network (CPMN) are used to study the EIA variations associated with the equatorial electrojet (EEJ). It is found in both the northern and southern hemispheres that the EIA crests manifest remarkable seasonal variations. The EIA maxima lag those of the EEJ by about 1.5-3 hours. The results reveal the time delay of both hemispheres to be asymmetry and vary with seasons. There are obvious relations between the intensity of EEJ and EIA as well as distance between the two crests. The associated correlation coefficients are about 0.52. However, no obvious seasonal and solar activity effects are found between the two observations.
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HSU, CHING LUH, and 徐慶陸. "SIMULATIONS OF TOMOGRAPHIC INVERSION IN THE IONOSPHERIC EQUATORIAL ANOMALY REGION." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/86443382566411444325.
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碩士國立中山大學
電機工程研究所
82
A SIMULATION STUDY HAS BEEN CARRIED FOR INVERTING THE EQUATORIAL HUMP FROM THE SLANT TOTAL ELECTRON CONTENT TAKEN FROM AN ENHANCED IONOSPHERIC MODEL. THE EXAMPLES SHOW PEAK LATITUDE IS MORE ACCURATELY DETERMINED THAN PEAK HEIGHT AND PEAK MAGNITUDE EVEN SUFFERING POOR INITIAL GUESS AND NOISE DETERIORATION. TO DETERMINE PEAK HEIGHT AND PEAK MAGNITUDE, THE SELECTION OF INITIAL BACKGROUND PROFILE IS CRUCIAL. INCONSISTENCY OF MEASURED SLANT TOTAL ELECTRON CONTENT AND INITIAL GUESS INTRODUCE DEFORMATION INTO RECONSTRUCTED IMAGE. FUTHER WORK IS NEEDED TO INVERT THE HUMP OPTIMALLY.
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Wen, Ku Wei, and 古惠文. "The Numerical Simulation of Irreqularities in Ionospheric Equatorial F Region." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/60601802453846975994.
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Alken, Patrick. "Modeling equatorial ionospheric currents and electric fields from satellite magnetic field measurements." Thesis, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3354556.
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Ko, Chen-Po, and 柯鎮波. "Investigation of the Equatorial F-region Ionospheric Irregularities using COSMIC/FORMOSAT-3." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/99712301251793745053.
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博士國立中央大學
太空科學研究所
98
The observations of the GPS occultation sensors onboard the six constellation satellites of COSMIC/FORMOSAT-3 are able to provide the truly global measurements of the ionosphere every day (~2000 occultation measurements). The large data set enables us a statistically correlative study of electron density depletion and GPS L1 scintillation, thus allows the global and altitudinal distributions of irregularity to be examined. In this thesis we will focus on the longitude sector (0o ~75oW) where the South Atlantic magnetic Anomaly (SAA) is located to study the morphology of equatorial F-region irregularity (EFI). The SAA longitude sector is selected because of its unique geomagnetic configuration and because of the constant existence of energetic particle precipitation in SAA. From the statistical analyses of the ionospheric electron density and scintillation S4 index data from FORMOSAT-3/COSMIC during 2007~2008, we have obtained the following results: (1) Under solar minimum and geomagnetic quiet conditions, post sunset EFI/scintillation events are found to concentrate in the SAA longitude sector during northern winter months (D-months), but nearly disappeared in the same longitude sector during the opposite season (J-months). (2) The D-months’ average pattern of EFI reveals that most of irregularities occurred in the bottom side F-region (200~350 km altitudes) and at low magnetic latitudes adjacent to the locations of the maximum post-sunset Nmax and Hmax. (3) Strong spatial correlations are found to exist among the sunset terminator, the westward declined geo-magnetic field, strong scintillation event, and density depletion in the SAA longitude sector only during D-months, where the E-region sunset terminator is most possibly parallel to the magnetic field direction at equatorial latitudes. (4) Two sources of ionization are considered to likely contribute to the post-sunset electric field enhancements at equatorial latitudes of the SAA longitude sector by means of creating ionospheric conductivity gradients. The first is solar radiation which can cause longitudinal conductivity gradients near the sunset terminators. The second is energetic particle precipitation which can cause conductivity gradients in the vicinity of SAA. (5) The combination of horizontal density gradients with anti-parallel (north-eastward) neutral winds during D-months can contribute additional growth rate to the EFI generation. These COSMIC observations not only confirm that the sunset equatorial electrodynamics plays a key role in controlling the seasonal and longitudinal occurrences of the quiet time EFI, but also reveal that seasonally dependent ionospheric responses to the energetic particle precipitation in SAA can affect considerably the morphology of EFI in the SAA longitude sector. We have demonstrated in this thesis that the continuously global occultation measurements from COSMIC/FORMOSAT-3 provide useful 3D data for the study of ionospheric irregularities. The morphology and the generation mechanisms of the equatorial F-region irregularities are critically important to the space weather research.
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Tsai, Ho-Fang, and 蔡和芳. "A Study of the Ionospheric Equatorial Anomaly by Using the Global Positioning System." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/76984127918843396685.
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博士國立中央大學
太空科學研究所
87
The global positioning system (GPS) has global long-term observation data and high spatial and temperal resolutions, which is an ideal tool to investigate large-scale ionospheric variations. In this dissertation, a study of the ionospheric equatorial anomaly in total electron content (TEC) has been developed by using the GPS to investigate the seasonal variations, solar eclipse effects, and magnetic storm effects. Combination of dual-frequency observables of psudoranges and carrier phases are employed to develop a GPS-TEC observtaion technique and then construct a 3-dimensional (3D) TEC distribution in time and latitude. Therefore, the ionospheric variability in TEC magitude and spatial distribution over the geomagnetic equatorial, equatorial anomaly, and even midlatitude regions are investigated. Observations for seasonal variations in the ionospheric northern and southern equatorial anomaly region in 1997 show that the TECs in equinotical seansons are greater than those in solstice seasons and a clear winter anomaly occurs in the northern hemisphere but not in the southern hemisphere. The asymmetry in the winter anomaly could be caused by different locations of the sub-solar points in summer and winter resulting in energy input imbalance between southern and northern hemispheres in this region. The appearing time of the equatorial anomaly crests are the earliest in winter, later in equinoxes, and the latest in summer. The two crests move significantly equatorward in winter but moderately poleward in summer and autumn. The appearing time and location of the two crests could be explained by combination of two theories: 1. A transequatorial neutral wind blowing from summer hemisphere to winter hemisphere; 2. The thermosphere-ionosphere-plasmasphere coupling which drives the equatorward thermospheric neutral wind in winter high latitude prevailing the poleward wind in low latitude. In the ionospheric transient variability, two solar eclipse events on October 24, 1995 and March 9, 1997 occuring in the Pacific-Asian region have been examined. Results show that the solar eclipse effects occur throughout the geomagnetic equatorial, equatorial anomaly, and midliatitude regions, and lasted many hours after the maximum occultation. Four features of the effects named pre-ascension (PA), major depression (MD), sunset ascension (SA), and secondary depression (SD) are observed during the eclipse days. A detailed study shows that in geomagnetic low latitudes, PA is possibly related to the locations of the equatorial anomaly crest. The latitudinal location, amplitude, and occurrence time of MD suggest that the fountain effect is essential. SA and SD occuring in geomagnetic equatorial and low latitudes and appearing respectively before/around and after local indicate that in addition to the day-to-day variations, the prereversal enhancement plays an important role. The effects of geomagnetic storm on ionospheric TEC have also been investigated by using the GPS data during two observations on January 10 and may 15, 1997, respectively. It is found that after the onset of sudden storm commencement (SSC), the equatorial anomaly crests move poleward, and the daytime TEC is significantly reduced one day after SSC. The penetration effect and distrubed dynamo mechanism in ionospheric electric fields are proposed to explain the above phenomena.
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Hartman, William Andrew. "Longitudinal and seasonal variations in the topside equatorial vertical ion drift near 0600, 0930, 1800 and 2130 LT /." 2007. http://proquest.umi.com/pqdweb?did=1296113141&sid=1&Fmt=2&clientId=10361&RQT=309&VName=PQD.
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Comberiate, Joseph Michael. "Tomographic imaging and characterization of ionospheric equatorial plasma irregularities with the Global Ultraviolet Imager /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3250228.
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Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1171. Adviser: Farzad Kamalabadi. Includes bibliographical references (leaves 108-114) Available on microfilm from Pro Quest Information and Learning.
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Tsai, Her-Chan, and 蔡和展. "On the Relationship between Equatorial Electrojet and Ionospheric Scintillation measured by FORMOSAT-3/COSMIC." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/n5k36y.
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碩士國立中央大學
太空科學研究所
97
In the day time equatorial ionosphere, there has been often observed a strong eastward current which is called Equatorial Electro-Jet (EEJ). According to the Ampere’s law, the current can induce the magnetic variations in its surroundings. Therefore scientists use magnetic observatories to measure the changes of magnetic field caused by EEJ and study the morphology of Equatorial electrojet. This thesis used the magnetic observatories’ data of International Real-time Magnetic Observatory Network to study the variations of magnetic field caused by Equatorial electrojet. Then we compared the Equatorial electrojet with ionosphere scintillations (represented by S4 values) detected by the FORMOSAT-3 satellites. The main task of this thesis consists of two parts. The first part is to study the morphology of EEJ, while the second part deals with the comparisons between EEJ and ionospheric scintillations. The main purpose of this thesis is using 2007 data sets to study the relationship between EEJ and the magnetic field variations affected by the EEJ under the following conditions: during the days of equinox and solstice; during 10 quiet days near the spring equinox; quiet times during the spring season; and on the May 23 storm day. From analyses of the magnetic field variations affected by EEJ, we found that there existed a seasonal variation in the morphology of EEJ. The seasonal (2007 spring) average location of EEJ is during 9 to 14 LT and ranges from the magnetic latitude 2o N to 3.15o S, while the maximum induced ∆H was about 116 nT. From the statistical comparison between EEJ and scintillation we have the following results: on spring equinox day positive correlation was found between their intensities; 10 days’ and seasonal averages reveal that stronger scintillations occurred near the boundary of EEJ. Moreover, from the comparison of the observations on storm day and quiet days we have the following findings: on storm day the EEJ current has changed it’s direction from that of quiet day pattern; and the average S4 is generally increased in the storm time EEJ region. Both EEJ and ionosphere scintillation change coherently when they have magnitude variations.
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Huang, Jyun-Ying, and 黃俊穎. "A modeling study of the ionospheric equatorial anomaly based on the FormoSat-3/COSMIC data." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/er73ke.
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碩士國立中央大學
太空科學研究所
97
The TaiWan Ionospheric Model (TWIM) is a numerical and phenomenological model of global ionospheric electron density (Ne) and is constructed from monthly-weighted and hourly vertical Ne profiles retrieved from FormoSat3/COSMIC GPS radio occultation measurements. TWIM can also provide global F2-layer critical frequency (foF2), peak density height (hmF2), and scale height (HF2) maps to study features of equatorial ionospheric anomaly (EIA). The modeling study investigates the diurnal and seasonal variations of EIA and specifically attempts to account for the latitudinal and longitudinal structures. This paper also shows that the neutral winds could cause the north-south asymmetries and longitudinal variation. Furthermore, the phenomena of EIA were also varied with the solar activity. The foF2 values in 2007 are higher than those in 2008 generally, with the exception in March. This variation and exception match to the different of the observational sunspot number between 2007 and 2008.
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Wu, Meng-Ying, and 吳孟穎. "Phase Scintillation of GPS Signals due to Ionospheric Irregularities in the Equatorial and Polar Regions." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/75e9yv.
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碩士國立臺灣大學
電信工程學研究所
104
Phase scintillations of GPS signals caused by ionospheric irregularities in the equatorial and polar regions are simulated and analyzed. The electron density irregularities in the ionosphere are modeled with different spectra, and realized with a Monte-Carlo technique. A parabolic wave equation (PWE) technique is then applied to compute the field distribution of GPS signals as they propagate through the ionosphere. The simulated phase scintillation in high-latitude regions is much more obvious than that in the equatorial region.
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Chen, M. C., and 陳孟聰. "A Study of Bubble & Patch in Equatorial Ionosphere F-Layer." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/45642579534323846240.
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Fern, C. L., and 馮志龍. "Simulations of Pure Two-Stream Waves in the Equatorial E-region Ionosphere." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/74234128445303163268.
Full textAbstract:
博士國立中央大學
太空科學研究所
89
At the altitude range of 95∼110 km in the equatorial E-region ionosphere, a large current in the magnetic equator called the equatorial electrojet is created by a dynamic process involving atmospheric tides. The equatorial electrojet causes the medium to be unstable to generate plasma waves. Radar observations have shown the existence of two classes of plasma waves, called typeⅠand typeⅡ. The typeⅠwave resulting from the two-stream instability is also called two-stream wave. In this paper, the behavior of two-stream wave in the plane perpendicular to the Earth's magnetic field is simulated by a two-dimensional fluid model simulation code in which the electron inertia is neglected while the ion inertia is retained. We consider the suitable two-dimensional simulation space (27×54m ) and successfully excite the dominant 3-meter wave compatible with VHF radar echoes. The analysis methods of two-dimensional Fourier series are derived to express the time variation of mode powers and ω spectra. From the series of simulation results for two-stream waves in the equatorial E-region ionosphere, we have studied the dispersion relations, the resonant coupling, and the echo power variation with the zenith angle rate of approximately 0.3(dB/degree). We have also studied the vertical small-scale waves developed from the distortions of the dominant waves. The vertical waves will cause dominant waves to turn away from the electrojet drift direction (E×B ). The important point about the development of vertical modes is asymmetry. We find that the spectral asymmetry depends on the scale size of plasma waves, that is, the large-scale waves (above 3 meters) propagate in the k‧E＜0 region, and the small-scale (smaller than 3 meters) propagate in the k‧E＞0 region. The simulation result of up-down asymmetry for 3-meter wave is consistent with the radar observations. We believe that the background polarization electric field E driving the electrojet is responsible for the spectral asymmetries. In the same time, owning to the strong and fixed background polarization electric field E , the wave frequency depends only on horizontal wave number Kx . Therefore, the phase velocities of many obliquely propagating two-stream waves (Kz≠0 ) are below the value predicted by linear theory, and this characteristic is prominent especially for large-scale waves.
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Hickey, Dustin A. "Spatial characteristics of the midnight temperature maximum and equatorial spread F from multi-instrument and magnetically conjugate observations." Thesis, 2018. https://hdl.handle.net/2144/33120.
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The upper atmosphere, a region above ~85 km called the ionosphere and thermosphere, has been studied extensively for over one hundred years. Measurements were often considered in isolation, but today, advances in technology and ground-based distributed arrays have allowed concurrent multi-instruments measurements. In this dissertation, I combine measurements from all-sky imagers (ASIs), coherent scatter radars, incoherent scatter radars (ISRs), and Fabry-Perot interferometers (FPIs). I focus on two phenomena, the midnight temperature maximum (MTM) and equatorial spread F (ESF), using observations from equatorial to mid-latitudes. The spatial characteristics of these phenomena are not fully understood. I combine observations at various latitudes and longitudes to extend MTM detection to mid-latitudes. I present the first simultaneous detections of the MTM at multiple altitudes and latitudes over North America and the first observations below the F-region peak using the Millstone Hill Observatory ISR in a south pointing, low-elevation mode. The MTM can also be observed with an ASI and I present concurrent measurements of the MTM with an ASI and ISR. The Whole Atmosphere Model, a global circulation model, was found to be consistent with these observations. This further verifies that the MTM is partially created by lower atmospheric tides, demonstrating coupling between the lower and upper atmosphere. In addition to the MTM, I investigate different aspects of ESF using ASIs concurrently with other instruments. I compare various scale sizes (sub-meter to kilometers) using coherent scatter radar and an ASI and conclude that the lower hybrid drift instability causes radar echoes to occur preferentially on the western wall of large-scale depletions. The source of day-to-day variability in ESF is not fully known but I show that one driver may be large-scale wave structures (~400 km) that modulate the development of ESF. Finally, I compare concurrent observations of ESF plasma depletions with ASIs at magnetically-conjugate foot points and show how the magnitude and structure of the Earth’s magnetic field is responsible for differences in the morphology and velocity of these depletions. In summary, I have used multi-instrument observations of ESF and the MTM to provide a deeper understanding of the dynamics of the upper atmosphere.
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Huang, Chi-Ruei, and 黃啟瑞. "Development abd Applications of Tomography technique to investigate the ionosphere in the Equatorial Aomaly Region." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/09802608293583889837.
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博士國立中央大學
電機工程學系
85
Abstract The type of Computerized Ionospheric Tomography (CIT) studied in this thesis is suitable for investigating ionospheric structures of horizontal scales of several hundred kilometers or greater. One region where these large-scale ionospheric variations occur daily is the Equatorial Anomaly (EA) region. In this thesis this technique was used to study the ionospheric electrodynamics in the EA region. First, improvement for the differential Doppler measurement technique was implemented and the CIT technique was modified specially for the applications in the EA region. In addition, observational data deduced from "Low-latitude Ionospheric Tomography Network (LITN)" were used to investigate the day to day variations and the low latitude ionosphere. Finally, the response of the low latitude ionosphere during Solar Eclipse was studied using the modified CIT technique.A modified ionosonde-Doppler method was developed to deduce the initial Doppler phase. This technique combined ionosonde and Differential Doppler records to determine the "unknown constant." Currently, several CIT research groups combined Total Electron Content (TEC) data with differential Doppler phase records to develop the so called three dimensional (3D) CIT technique. We found that the TEC obtained from Global Positional Satellite (GPS) measurements were in general 2-3 times greater than the actual values between sunset and noontime of the next day. Consequently, it should be carefully checked when using TEC derived from GPS measurements. The geometry of CIT is a "limited angle tomography" problem. The best way to develop the CIT technique is to include "A priori information" in the image reconstruction procedure for compensating the "missing horizontal ray" problem in CIT. For this reason, the thesis proposed a combination method to make use the "a priori information" such as ionosonde records, ionosphere model, empirical F2 peak distribution and the vertical TEC derived from differential Doppler records. This method generated an image as the initial guess for iterative reconstruction algorithm. Model simulations and reconstructions for measured data proved that this method can be used for reconstructing the electron density distributions in the EA region. In addition, a method for verification of the reconstructed image with global ionosonde data was proposed and implemented in the thesis..Previous studies revealed that low-latitude ionosphere experiences day to day variations. Initial investigations utilizing multiple Differential Doppler records provided by the LITN facility revealed that the latitudinal distribution of vertical TEC depends on (1)the conversion height of ionosphere, (2)the location of receiver, (3)integration constant and (4)the number of receiver. In this thesis, the modified multi-station method and reconstruction algorithm were used to investigate the day to day variations of October, 1994 and October 1995. It revealed that the crest started to develop after sunrise and decay after the sunset during low solar activity epoch, but persisted late into the night during the solar maximum. It was characterized by a trough at the magnetic equator and one hump at about 10oN of magnetic equator around 14:00 Local Standard Time in this season. The advantages of Computerized Ionospheric Tomography technique were not only the capability to observe the large scale latitudinal TEC distributions but also the possibility to provide the electron density profiles for studying the ionospheric electrodynamics.The investigation during the Total solar eclipse of October 24, 1995 revealed that the low-latitude ionosphere was affected by the combination of electrodynamics and photochemical processes. Two-dimensional (2D) images of ionospheric electron density during the eclipse period were reconstructed. These images and the corresponding results from a nearby ionosonde were compared with those for a reference day. It was shown that during the eclipse day the ionosphere experienced several episodes of electron density enhancement and depression. However, due to large day to day variation, only two depressions were identified as caused by solar eclipse effects. (1) The largest electron density depression occurred roughly 2 hours after the maximum obscuration at approximately 12oN geomagnetic latitude and on both the bottom and topside ionosphere. (2) The second depression occurred about 4 hours after maximum obscuration at approximately 5.5oN and mainly on the topside ionosphere. The former might have been caused by complicated photochemical and ion transportation processes, and the latter could come from the transportation delay of ion from the conjugate point. These observations were interpreted within the framework of ionospheric dynamics in the equatorial anomaly region.(Keywords: Tomography, image reconstruction algorithm, Ionosphere, Equatorial Anomaly, Low-latitude Ionospheric Tomography Network, Differential Doppler, Total Electron Content, Solar Eclipse)
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Liu, Yen Hung, and 劉彥宏. "Using ROCSAT-1 In-situ Data to Study the Radiowave Scintillation Phenomenon in the Equatorial to Low-Latitude Ionosphere." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/30280497356505452744.
Full textAbstract:
博士國立中央大學
電機工程學系
101
The global/seasonal/local-time distributions of scintillation occurrence rate have been obtained from the in-situ density measurement of ROCSAT-1 during moderate to high solar activity periods of 2000 to 2003. The scintillation was obtained with a modified procedure of the thin-phase screen model of Rino reported in Wernik et al. [2007]. The distribution of the S4 index for the weak scintillation (S4<0.3) is almost identical to that of the equatorial irregularity distribution reported in the literature. However, as the scintillation level increases (0.3< S4<0.6), the latitudinal distribution moves to the equatorial ionization anomaly (EIA) region. In addition, the distributions of the outer scale values that are valuable for the study of physical evolution of the irregularity structure are also obtained. The occurrence distribution of scintillation activity with several parameters such as dip-latitude, longitude, local time, solar activity, and geomagnetic activity during different seasons are presented and discussed in the report. In addition, a special case of coincident observation that occurred on 24 March 2000 between the irregularity structure measured by ROCSAT-1 and the scintillation experiment at the Ascension Island has been studied. The study of scintillation statistics is carried out first and the results shows that the Nakagami distribution can portray the scintillation intensities with S4 up to 1.4 for the L-band scintillation. Moreover, the departure of frequency dependence of S4 predicted by the weak scintillation is noticed due to the multiple scattering effect. The measurements between the satellite and scintillation data are then compared against each other to study the similarity in the gross feature between the characteristics of irregularity structure and the scintillation variation. The causal relationship between the fluctuation of ion density and the scintillation variation is obtained. The coincident observations are also validated by the PEM simulation result.
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Yang, Jhih-yung, and 楊智源. "Electron density profiles in the equatorial ionosphere observed by the FORMOSAT-3/COSMIC and a digisonde portable sounder at Jicamarca." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/34aet5.
Full textAbstract:
碩士國立中央大學
太空科學研究所
97
The FORMOSAT-3/COSMIC (F3/C) program applies the radio occultation technique to derive the electron density profiles, using the GPS occultation experiment (GOX) onboard the F3/C. In this study, we examine the ionospheric data concurrently observed by the F3/C and Digisonde Portable Sounder (DPS) at Jicamarca (12°S, 283°W, 1°N geomagnetic) in 2007. First, we use the criteria to choose the F3/C data that have the physics meanings (For example: the F3/C F2-peak height, HmF2, must be higher than 200KM). Then, we compare the F2-peak density (NmF2) and HmF2 of F3/C with those of Jicamarca DPS in different time periods. Results show that the F3/C generally underestimates the values of NmF2 and HmF2. The underestimates are mainly affected by the seasonal variation in the horizontal electron density. On the other hand, the F3/C overestimates the NmF2 in the afternoon period, especially at about 14:00LT. The greater electron density at the equatorial ionization anomaly accounts for the overestimate.
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Mays, Mona Leila. "The study of interplanetary shocks, geomagnetic storms, and substorms with the WINDMI model." 2009. http://hdl.handle.net/2152/10703.
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WINDMI is a low dimensional plasma physics-based model of the coupled magnetosphere-ionosphere system. The nonlinear system of ordinary differential equations describes the energy balance between the basic nightside components of the system using the solar wind driving voltage as input. Of the eight dynamical variables determined by the model, the region 1 field aligned current and ring current energy is compared to the westward auroral electrojet AL index and equatorial geomagnetic disturbance storm time Dst index. The WINDMI model is used to analyze the magnetosphere-ionosphere system during major geomagnetic storms and substorms which are community campaign events. Numerical experiments using the WINDMI model are also used to assess the question of how much interplanetary shock events contribute to the geoeffectiveness of solar wind drivers. For two major geomagnetic storm intervals, it is found that the magnetic field compressional jump is important to producing the changes in the AL index. Further, the WINDMI model is implemented to compute model AL and Dst predictions every ten minutes using real-time solar wind data from the ACE satellite as input. Real-Time WINDMI has been capturing substorm and storm activity, as characterized by the AL and Dst indices, reliably since February 2006 and is validated by comparison with ground-based measurements of the indices. Model results are compared for three different candidate input solar wind driving voltage formulas. Modeling of the Dst index is further developed to include the additional physical processes of tail current increases and sudden commencement. A new model, based on WINDMI, is developed using the dayside magnetopause and magnetosphere current systems to model the magnetopause boundary motion and the dayside region 1 field aligned current which is comparable to the auroral upper AU index.text