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Ssessanga, Nicholas. "Development of an ionospheric map for Africa." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1011498.
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This thesis presents research pertaining to the development of an African Ionospheric Map (AIM). An ionospheric map is a computer program that is able to display spatial and temporal representations of ionospheric parameters such as, electron density and critical plasma frequencies, for every geographical location on the map. The purpose of this development was to make the most optimum use of all available data sources, namely ionosondes, satellites and models, and to implement error minimisation techniques in order to obtain the best result at any given location on the African continent. The focus was placed on the accurate estimation of three upper atmosphere parameters which are important for radio communications: critical frequency of the F2 layer (foF2), Total Electron Content (TEC) and the maximum usable frequency over a distance of 3000 km (M3000F2). The results show that AIM provided a more accurate estimation of the three parameters than the internationally recognised and recommended ionosphere model (IRI-2012) when used on its own. Therefore, the AIM is a more accurate solution than single independent data sources for applications requiring ionospheric mapping over the African continent.
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Oyeyemi, Elijah Oyedola. "A global ionospheric F2 region peak electron density model using neural networks and extended geophysically relevant inputs." Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005255.
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This thesis presents my research on the development of a neural network (NN) based global empirical model of the ionospheric F2 region peak electron density using extended geophysically relevant inputs. The main principle behind this approach has been to utilize parameters other than simple geographic co-ordinates, on which the F2 peak electron density is known to depend, and to exploit the technique of NNs, thereby establishing and modeling the non-linear dynamic processes (both in space and time)associated with the F2 region electron density on a global scale. Four different models have been developed in this work. These are the foF2 NN model, M(3000)F2 NN model, short-term forecasting foF2 NN, and a near-real time foF2 NN model. Data used in the training of the NNs were obtained from the worldwide ionosonde stations spanning the period 1964 to 1986 based on availability, which included all periods of calm and disturbed magnetic activity. Common input parameters used in the training of all 4 models are day number (day of the year, DN), Universal Time (UT), a 2 month running mean of the sunspot number (R2), a 2 day running mean of the 3-hour planetary magnetic index ap (A16), solar zenith angle (CHI), geographic latitude (q), magnetic dip angle (I), angle of magnetic declination (D), angle of meridian relative to subsolar point (M). For the short-term and near-real time foF2 models, additional input parameters related to recent past observations of foF2 itself were included in the training of the NNs. The results of the foF2 NN model and M(3000)F2 NN model presented in this work, which compare favourably with the IRI (International Reference Ionosphere) model successfully demonstrate the potential of NNs for spatial and temporal modeling of the ionospheric parameters foF2 and M(3000)F2 globally. The results obtained from the short-term foF2 NN model and nearreal time foF2 NN model reveal that, in addition to the temporal and spatial input variables, short-term forecasting of foF2 is much improved by including past observations of foF2 itself. Results obtained from the near-real time foF2 NN model also reveal that there exists a correlation between measured foF2 values at different locations across the globe. Again, comparisons of the foF2 NN model and M(3000)F2 NN model predictions with that of the IRI model predictions and observed values at some selected high latitude stations, suggest that the NN technique can successfully be employed to model the complex irregularities associated with the high latitude regions. Based on the results obtained in this research and the comparison made with the IRI model (URSI and CCIR coefficients), these results justify consideration of the NN technique for the prediction of global ionospheric parameters. I believe that, after consideration by the IRI community, these models will prove to be valuable to both the high frequency (HF) communication and worldwide ionospheric communities.
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Stolle, Claudia, Stefan Schlüter, Christoph Jacobi, Norbert Jakowski, and Armin Raabe. "Monitoring of a polar plasma convection event with GPS." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217497.
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When L-band radio waves of space based systems such as Global Positioning System (GPS) travel trough the ionosphere and plasmasphere their ray paths are perturbed due to the free electrons. Since the last decade these integrated measurements are used to map the ionosphere for navigational and scientific investigations. In November 2001 a polar plasma convection like ionospheric event has been recognised in vertical TEC maps produced with GPS data. This event on the one hand is shortly compared with the behaviour of the Interplanetary Magnetic Field (IMF) to which it may be related according to former publications. On the other hand the 3-dimensional tomography applying also GPS data is tested on its capability to reconstruct this ionospheric event in the European sector. The different mappings of the two monitoring methods are comparedWenn L-Band-Radiowellen raumgestützter Navigationssysteme wie das Global Positioning System (GPS) die Ionosphäre oder Plasmasphäre durchlaufen, werden Ihre Strahlwege durch die freien Elektronen verändert. Seit dem letzten Jahrzehnt verwendet man diese integrierten Messungen, um die Ionosphäre im Interesse der Navigation und der Wissenschaft abzubilden. Am Beispiel eines Ereignisses vom November 2001 wurde eine polare Plasmakonvektion in der Ionosphäre durch vertikale TEC –Karten (Total Electron Content), die ebenfalls mit Hilfe von GPS Daten erstellt werden, abgebildet. Einerseits wurde das Ereignis der Plasmakonvektion mit dem Verhalten des Interplanetaren Magnetischen Feldes (IMF) kurz verglichen und auf ihren Zusammenhang hin untersucht. Auf der anderen Seite wurde anhand dieses Ereignisses die Methode einer über den europäischen Raum aufgespannten auf GPS–Daten basierenden 3-dimensionale Tomographie auf ihre Reproduzierbarkeit hin geprüft. Die zwei verschiedenen Methoden des Ionosphärenmonitorings werden verglichen
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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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Haggard, Raymond. "The effects of particle precipitation on the ionosphere in the South Atlantic Anomaly Region." Thesis, Rhodes University, 1994. http://hdl.handle.net/10962/d1005248.
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The first ground based observations of aeronomic phenomena in the South Atlantic Anomaly Region are presented. These data show that enhancements in foF2 and foE can be directly attributed to precipitated electron energy fluxes in the Anomaly Region. The regular occurrence of particle induced sporadic-E ionization is also presented together with the first measurable 391.4 nm airglow radiation of about 16 R. The first comprehensive survey of energy fluxes carried by energetic particles using satellites is also presented for both daytime and nighttime as well as the seasonal fluctuations. We found that the nocturnally precipitated electron energy fluxes varied between 1 x 10⁻⁴ and 38 x 10⁻⁴ erg cm²s⁻¹, depending upon magnetic activity and season, whereas the daytime precipitated electron energy fluxes tended to vary between 1 x 10⁻³ and 8 x 10⁻³ erg cm⁻²s⁻¹, with a tendency to decrease during magnetically active periods. Electron density and temperature contours as well as NO⁺ and 0⁺ ions contours for nighttime are also presented. The main conclusion of the study is that precipitating electrons provide a significant and sometimes dominant source of ionization in the ionosphere over the South Atlantic Anomaly Region.
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Banola, S. "Some characteristics of ionospheric irregularities at low latitudes deduced from VHF scintillation measurements." Thesis, IIG, 2001. http://localhost:8080/xmlui/handle/123456789/1574.
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Gavrilov, Nikolaj M., Christoph Jacobi, and Dierk Kürschner. "Drifts and their short-period perturbations in the lower ionosphere observed at Collm during 1983 - 1999." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-215386.
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Estimations of the intensity of short-period perturbations of the horizontal drift velocity at 80 - 110 km altitude are made using data from the regular low-frequency D1 ionospheric reflection observations at Collm, Germany (52° N, 15° E) for the period 1983 - 1999. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales between 0.7 and 3 hours. The results are compared with the mean drift analyses in order to study the interaction between short-period perturbations and the mean circulation. The average monthly variances of short-period perturbations of the zonal velocity near 80 km altitude show a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards spring, and another maximum of perturbation variances in autumn appears at altitudes near and above 100 km. The seasonal changes of variances of the meridional velocity show maximum values in spring and summer, also some indications for an increase of the summer maximum at altitudes larger than 100 km are found. The observed altitude changes of the seasonal variations of drift perturbation variances are consistent with some numerical calculations of the height structure of a spectrum of internal gravity waves in the middle and upper atmosphereDie Intensität kurzperiodischer Störungen der horizontalen Driftgeschwindigkeit im Höhenbereich zwischen 80 und 110 km wurde anhand der regulären D1 Langwellenreflexionsmessungen in Collm (52° N, 15° E), bestimmt. Verwendet wurden Daten der Jahre 1983 - 1999. Ein einfache numerische Filter basierend auf den Unterschieden aufeinanderfolgender halbstündiger Windmittelwerte wurde verwendet, um Störungen im Zeitbereich von 0.7 - 3 Stunden zu ermitteln. Die Ergebnisse wurden mit Analysen der mittleren Drift verglichen, um die Wechselwirkungen zwischen kurzperiodischen Störungen und der mittleren Zirkulation zu untersuchen. Die mittlere monatliche Varianz der kurzperiodischen Störungen der Zonalgeschwindigkeit bei etwa 80 km zeigt ein Hauptmaximum im Sommer und ein schwächeres Maximum im Winter, wobei die Minima während der Aquinoktien auftreten. In grösseren Höhen verschiebt sich das Sommermaximum zum Frühjahr hin, und in Höhen über 100 km erscheint im Herbst ein weiteres Maximum. Der Jahresgang der meridionalen Windstörungen zeigt maximale Werte in Frühjahr/Sommer, und es sind auch Hinweise auf eine Verstärkung des Sommermaximums oberhalb von 100 km zu finden. Die gemessenen Höhenänderungen im Jahresgang der kurzperiodischen Driftschwankungen entsprechen numerischen Ergebnissen der Höhenabhängigkeit interner Schwerewellen in der mittleren und oberen Atmosphäre
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Koparkar, P. V. "Studies in ionospheric physics with special reference to the ionospheric irregularities and VHF scintillations." Thesis, IIG, 1985. http://localhost:8080/xmlui/handle/123456789/1560.
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Johnson, Rosie Eleanor. "Infrared observations of Jupiter's ionosphere." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/42409.
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In this thesis I have used infrared observations of Jupiter to investigate the flows of ions in the ionosphere and how they are coupled to the ionospheric heating in the auroral regions, determining the drivers of the heating and how they are related to the thermosphere and the magnetosphere. I investigated the H3+ line-of-sight velocity in the mid-to-low latitude region, derived from the Doppler shift of the Q(1,0-) emission line taken by IRTF-CSHELL. No evidence of flows in the region of the H Ly-α bulge predicted by a global circulation model were measured, and the H3+ ions in the mid-to-low latitude region were found to be corotating. Using observations taken by VLT-CRIRES, polar projections of the intensity and line-of-sight velocity of the H3+ ions in Jupiter’s northern auroral region were created. This revealed the ionospheric flows and how they relate to different morphological regions of the northern aurora. These flows vary from extremely sub-rotational to super-rotational, and the drivers of the flows range from the solar wind and magnetospheric interaction to a potential thermospheric driver. The same set of VLT-CRIRES observations are then used to derive the rotational temperature, column density, and total emission of the H3+ ions in the northern auroral regions. These properties were mapped onto polar projections, which revealed changes in temperature during the observations (over a short period of ~80 minutes). The changes in temperature could be caused by local time changes in particle precipitation energy, or they could be caused by the thermospheric response to a transient enhancement of solar wind dynamic pressure, as predicted by models. By comparing all of the H3+ properties, the complex interplay between heating by impact from particle precipitation and Joule heating, as well as cooling by the H3+ thermostat effect was revealed.
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Panicciari, Tommaso. "Multiresolution tomography for the ionosphere." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.698998.
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The ionosphere is a dynamic and ionized medium. Specification of the ionospheric electron density is important for radio systems operating up to a few GHz. Such systems include communication, navigation and surveillance operations. Computerized Ionospheric Tomography (CIT) is a technique that allows specification of the electron density in the ionosphere. CIT, unlike medical tomography, has geometric limitations such as uneven and sparse distribution of ground-based receivers and limited-angle observations. The inversion is therefore underdetermined and to overcome the geometric limitations of the problem, regularization techniques need to be used. In this thesis the horizontal variation of the ionosphere is represented using wavelet basis functions. Wavelets are chosen because the ground based ionospheric instrumentation is unevenly distributed and hence there is an expectation that the resolution of the tomographic image will change across a large region of interest. Wavelets are able to represent structures with different scale and position efficiently, which is known as Multi Resolution Analysis (MRA). The theory of sparse regularization allows the usage of a small number of basis functions with minimum loss of information. Furthermore, sparsity through wavelets can better differentiate between noise and actual information. This is advantageous because it increases the efficacy to resolve the structures of the ionosphere at different spatial horizontal scale sizes. The basis set is also extended to incorporate time dependence in the tomographic images by means of three-dimensional wavelets. The methods have been tested using both simulated and real observations from the Global Navigation Satellite System (GNSS). The simulation was necessary in order to have a controllable environment where the ability to resolve different scale structures would be tested. The further analysis of the methods required also the use of real observations. They tested the technique under conditions of temporal dynamics that would be more difficult to reproduce with simulations, which often tend to be valid in quiet ionospheric behaviors. Improvements in the detection and reconstruction of ionospheric structures were illustrated with sparse regularization. The comparison was performed against two standard methods. The first one was based on spherical harmonics in space, whilst the second relied on a time-dependent smoothing regularization. In simulation, wavelets showed the possibility to resolve small-scale structures better than spherical harmonics and illustrated the potential of creating ionospheric maps at high resolution. In reality, GNSS satellite orbits allow satellite to receiver datasets that traverse the ionosphere at a few hundred km per second and hence a long time window of typically half an hour may be required to provide observations. The assumption of an unchanging ionosphere is only valid at some locations under very quiet geomagnetic conditions and at certain times of day. For this reason the theory was extended to include time dependence in the wavelet method. This was obtained by considering two approaches: a time-smooth regularization and three-dimensional wavelets. The wavelet method was illustrated on a European dataset and demonstrated some improvements in the reconstructions of the main trough. In conclusion wavelets and sparse regularization were demonstrated to be a valid alternative to more standard methods.
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Kürschner, Dierk, and Christoph Jacobi. "Long-term behaviour of E-region nighttime LF reflection heights." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217519.
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The nighttime reflection height of low-frequency (LF) radio waves at oblique incidence is measured at Collm Observatory using 1.8 kHz sideband phase comparisons between the sky wave and the ground wave of a commercial 177 kHz LF transmitter. The measurements have been carried out continuously since September 1982, now allowing the analysis of trends and regular variations of the reflection height. In the time series is found a) a long-term negative trend and b) a solar cycle dependence, both confirming earlier measurements and theoretical estimations. Moreover, a significant oscillation of quasi-biennial period is visible in LF reflection heights, indicating a reaction of the midlatitude mesosphere/lower thermosphere region on the equatorial quasi biennial oscillationAm Observatorium Collm der Universität Leipzig werden die nächtlichen Reflexionshöhen von Langwellen auf 177 kHz unter Verwendung von Seitenbandinformationen in einem kleinen Bereich um 1.8 kHz gemessen. Die Messungen werden seit September 1982 durchgeführt und erlauben nunmehr Analysen von Langzeittrends und regulären Variationen der unteren Ionosphäre. Bei der Untersuchung der Zeitreihen fallen die folgenden Zusammenhänge auf: a)es existiert ein negativer Trend, welcher mit der Abkühlung der Stratosphäre in Zusammenhang steht, b) die Reflexionshöhe weist eine Modulation mit dem 11-Jährigen Sonnenfleckenzyklus auf und c) es ist eine deutliche quasi-zweijährige Schwingung sichtbar, die auf eine Kopplung der Mesosphäre und unteren Thermosphäre mit der äquatorialen Stratosphäre hinweist
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Pathan, Bashir Mohammed. "Studies of low latitude ionosphere through satellite radio wave propagation." Thesis, IIG, 1994. http://localhost:8080/xmlui/handle/123456789/1566.
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Amabayo, Emirant Bertillas. "Multi-instrument observations of ionospheric irregularities over South Africa." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1005261.
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The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes at Madimbo (30.88◦E, 22.38◦S), Grahamstown (33.32◦S, 26.50◦E) and Louisvale (28.51◦S, 21.24◦E). This study is intended to quantify the probability of the occurrence of F region disturbances associated with ionospheric spread F (SF) and L-band scintillation over South Africa. This study used available ionosonde data for 8 years (2000-2008) from the three South African stations. The SF events were identified manually on ionograms and grouped for further statistical analysis into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The results show that the diurnal pattern of SF occurrence peaks strongly between 23:00 and 00:00 UT. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown during 2001 and 2005, except for RSF which had peaks during autumn and spring during 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing sunspot number (SSN), with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study SF was evident in ∼ 0.03% and ∼ 0.06% of the available ionograms at Madimbo and Grahamstown respectively during the eight year period. The presence of ionospheric irregularities associated with SF and scintillation was investigated using data from selected Global Positioning System (GPS) receiver stations distributed across South Africa. The results, based on GPS total electron content (TEC) and ionosonde measurements, show that SF over this region can most likely be attributed to travelling ionospheric disturbances (TIDs), caused by gravity waves (GWs) and neutral wind composition changes. The GWs were mostly associated with geomagnetic storms and sub-storms that occurred during periods of high and moderate solar activity (2001-2005). SF occurrence during the low solar activity period (2006-2008)can probably be attributed to neutral wind composition changes.
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Da, Dalt Federico. "Ionospheric modelling and data assimilation." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665450.
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A New Ionospheric Model (ANIMo) based upon the physics of production, loss, and vertical transport has been developed. The model is driven by estimates of neutral composition, temperature and solar flux and is applicable to the mid-latitude regions of the Earth under quiet and moderate geomagnetic conditions. This model was designed to exhibit specific features that were not easy to find all together in other existing ionospheric models. ANIMo needed to be simple to use and interact with, relatively accurate, reliable, robust and computationally efficient. The definition of these characteristics was mostly driven by the intention to use ANIMo in a Data Assimilation (DA) scheme. DA or data ingestion can be described as a technique where observations and model realizations, called background information, are combined together to achieve a level of accuracy that is higher than the accuracy of the two elements taken separately. In this project ANIMo was developed to provide a robust and reliable background contribution. The observations are given by the Global Positioning System (GPS) ionospheric measurements, collected from several networks of GPS ground-station receivers and are available on on-line repositories. The research benefits from the Multi-Instrument Data Analysis System (MIDAS) [Mitchell and Spencer, 2003; Spencer and Mitchell, 2007], which is an established ionospheric tomography software package that produces three dimensional reconstructions of the ionosphere starting from GPS measurements. Utilizing ANIMo in support of MIDAS has therefore the potential to generate a very stable set-up for monitoring and study the ionosphere. In particular, the model is expected to compensate some of the typical limitations of ionospheric tomography techniques described by Yeh and Raymund [1991] and Raymund et al. [1994]. These are associated with the lack of data due to the uneven distribution of ground-based receivers and limitations to viewing angles. Even in regions of good receiver coverage there is a need to compensate for information on the vertical profile of ionisation. MIDAS and other tomography techniques introduce regularization factors that can assure the achievement of a unique solution in the inversion operation. These issues could be solved by aiding the operation with external information provided by a physical model, like ANIMo, through a data ingestion scheme; this ensures that the contribution is completely independent and there is an effective accuracy improvement. Previously, the limitation in vertical resolution has been solved by applying vertical orthonormal functions based upon empirical models in different ways [Fougere, 1995; Fremouw et al., 1992; Sutton and Na, 1994]. The potential for the application of a physical model, such ANIMo is that it can provide this information according to the current ionospheric conditions. During the project period ANIMo has been developed and incorporated with MIDAS. The result is A New Ionospheric Data Assimilation System (ANIDAS); its name suggests that the system is the implementation of ANIMo in MIDAS. Because ANIDAS is a data ingestion scheme, it has the potential to be used to perform not only more accurate now-casting but also forecasting. The outcomes of ANIDAS at the current time can be used to initialise ANIMo for the next time step and therefore trigger another assimilation turn. In future, it is intended that ANIMo will form the basis to a new system to predict the electron density of the ionosphere – ionospheric forecasting.
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Schlatter, Nicola. "Enhanced Radar Backscatter from the Ionosphere." Licentiate thesis, KTH, Rymd- och plasmafysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-116669.
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Incoherent scatter radars are powerful ground based instruments for ionospheric measurements. By analysis of the Doppler shifted backscatter spectrum, containing the signature of electrostatic plasma waves, plasma bulk properties are estimated. Occasionally, the backscattered radar power is enhanced several orders of magnitude above the thermal backscatter level. These enhancements occur during naturally disturbed ionospheric conditions and in ionospheric modi_cation experiments, where a powerful radio wave is incident on the ionospheric plasma. In both of the cases the non-linearity is thought to be turbulence of electrostatic Langmuir waves. The Langmuir turbulence theory and models account for many features of enhanced ionospheric radar backscatter reported on in the literature. During disturbed conditions, with precipitation of auroral electrons, Langmuir turbulence is thought to be driven by a low energy electron beam. Optical and radar observations of naturally enhanced radar backscatter indicate Alfvénic type of aurora during events reported on in the literature. However, contrasting conclusions have been drawn from optical observations. While some reports suggest that enhanced radar backscatter is observed at the edge of auroral structures others suggest that the enhanced backscatter region and auroral precipitation are co-located. Optical imagers with a narrow field of view resolve auroral structures with tens of meters scale size. The cross beam resolution of radars, however, is limited by the width of the radar beam, typically several kilometers wide at auroral altitudes. By using several radar receivers for observations - radar interferometry - the cross beam resolution is increased. Simultaneous observations of enhanced radar backscatter with radar interferometry and narrow field of view optical observations will increase the understanding of the physical processes involved and will make it possible to associate auroral structures with the enhanced radar backscatter. An interferometric radar receiver system has been built and a calibration technique for the system developed. In ionospheric modification experiments, the Langmuir turbulence is driven by a powerful electromagnetic wave incident on the ionosphere and electrons are significantly accelerated. The acceleration of electrons is not yet fully understood. Ionospheric modification experiments and ground based measurements, as reported on herein, contribute to the understaQC 20130131
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Homam, Mariyam Jamilah. "Radiowave propagation in the polar ionosphere." Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/10812.
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A dual-frequency GPS receiver, GSV4004B, has been installed at Alert, Canada since May 2008 to study the ionospheric variability at a high-latitude location. This Ionospheric Scintillation and TEC Monitor (GISTM) receiver is able to measure amplitude and phase scintillation, and also Total Electron Content (TEC). In addition, a High Frequency (HF) link has been established from Qaanaaq to Svalbard since March 2009 to study the channel characteristics, including Doppler spreads. This study covers from end of May 2008 to February 2011 where it was mostly during the minimum state of solar activity. During the period of where both GISTM and HF data were available (i.e. March 2009-July 2010), data from both links are compared to see any relation between TEC variations and scintillation effects and also Doppler spreads. Data from the GISTM receivers at Svalbard were also utilised. Winter months expectedly show lower mean vertical TEC (VTEC) than in other months. Higher mean VTEC was observed in 2010 that could be related to the increase of solar activity. In 2010, both small and large patches of moderate-high intensity were found to be more than twice as common in February and March than in other months. The difference in the occurrences of small patches between months of the same year was about 1-2% (for low intensity patches) and 1-10% (moderate-high intensity). This difference increased to 1-4% (low intensity) and 1-12% (moderate-high intensity) for large patches. UT dependence can be seen where ~80 large and ~300 small patches were identified ~1000 to 2000 UT from June to October in both 2008 and 2009, and they doubled in 2010. Amplitude scintillations index, S4 were very low where at least ~99% were between 0 and 0.1, which is insignificant. Meanwhile, phase scintillations index, σφ were from 0 to 0.1 rad for at least 93% of the time. The relationship of TEC fluctuations/increase and phase scintillations is complex. There are few events where phase scintillations occurred simultaneously with slant TEC increases, but this is not frequent. The magnitude of the irregularities was generally independent of geomagnetic indices, Interplanetary Magnetic Field (IMF) components, and local magnetic fields at Eureka and Resolute Bay. Monthly upper decile of Doppler spreads generally varied from 1 to 5.5 Hz. High upper decile normally occurred from around September/October to March, from ~0000 to 1700 UT on 6.95 and 8.01 MHz. The hourly upper decile reached up to 7-8.5 Hz (6.95 MHz) and 7-9.5 Hz (8.01 MHz). Upper decile on these frequencies was mostly 0.5-4.5 Hz larger in October 2010-February 2011 than in the same months of the previous year which possibly related to the increase in solar activity. However, Doppler spreads were generally independent of independent of geomagnetic indices, IMF components, and local magnetic fields. The relation between the irregularities observed via transionospheric link and HF link is also complex. Large TEC fluctuations/increases and/or phase scintillations observed on satellite(s) close to HF midpoint may correspond to either small or large Doppler spreads.
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Denton, Michael Harold. "Thermal balance of the topside ionosphere." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341853.
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Chatain, Audrey. "Aerosols-plasma interaction in Titan’s ionosphere." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASV022.
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Le système climatique de la lune de Saturne Titan est gouverné par la production intense d’aérosols organiques dans sa haute atmosphère. Ce phénomène s’est aussi certainement produit sur Terre au moment de l’apparition de la vie. Ces deux points motivent fortement les recherches sur les processus de formation et d’évolution des aérosols dans l’atmosphère de Titan. Les aérosols se forment et restent plusieurs semaines dans l’ionosphère, étendue d’environ 900 à 1200 km d’altitude. Cette région de l’atmosphère est ionisée par le rayonnement solaire UV et des particules énergétiques provenant de la magnétosphère de Saturne. Des espèces plasma très réactives sont ainsi présentes : des radicaux, des espèces excitées, des ions et des électrons. Dans un tel environnement, je me suis intéressée à l’interaction entre les aérosols organiques et le plasma.Ce phénomène est simulé en laboratoire avec une expérience développée à cet effet : des analogues des aérosols de Titan sont exposés à une décharge plasma en N2-H2. J’observe qu’à la fois les grains et la phase gaz évoluent. Les atomes H et N interagissent chimiquement avec les aérosols. Puis, du cyanure d’hydrogène (HCN) ainsi que d’autres molécules organiques sont éjectées en phase gaz par le bombardement ionique. Ces résultats mettent en évidence une contribution importante des processus hétérogènes dans l’ionosphère de Titan.Ma ré-analyse des données de la sonde de Langmuir de la mission Cassini a d’autre part révélé la présence d’une population d’électrons inattendue dans l’ionosphère, sous 1200 km d’altitude et côté jour, zone dans laquelle des ions lourds ont également été détectés. Ces électrons pourraient être émis par les aérosols, après collision avec un photon et/ou après chauffage par la chimie ionique très active dans cette régionThe climatic system of Saturn’s moon Titan is governed by the intense production of organic aerosols in its upper atmosphere. This phenomenon also certainly happened on Earth at the beginning of life. These two points strongly motivate research on the formation and evolution processes of the aerosols in the atmosphere of Titan. The aerosols form and stay several weeks in the ionosphere, between ~900-1200 km of altitude. This atmospheric layer is ionized by UV solar rays and energetic particles coming from Saturn’s magnetosphere, forming a plasma with very reactive species: radicals, excited species, ions and electrons. In such an environment, the main question I tackle is how the organic aerosols interact with the plasma species.The phenomenon is simulated in the laboratory with a plasma setup developed on purpose: analogues of Titan aerosols are exposed to a N2-H2 plasma discharge. Both an evolution of the solid and the gas phase are observed. H and N atoms chemically interact with the aerosols. Then, hydrogen cyanide (HCN) and other organic molecules are ejected in the gas phase by ion sputtering. These results highlight an important contribution of heterogeneous processes in Titan’s upper atmosphere.My re-analysis of the Cassini Langmuir probe data revealed the presence of an unexpected electron population in the ionosphere, below 1200 km and on the day-side, where heavy ions are also detected. These electrons could be emitted by the aerosols, after collision with a photon, and/or heating by the active ion chemistry
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Barjatya, Aroh. "Langmuir Probe Measurements In The Ionosphere." DigitalCommons@USU, 2007. https://digitalcommons.usu.edu/etd/274.
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Electric probes have been the primary instruments for the in situ investigation of plasma parameters in the Earth’s ionosphere. This dissertation is a compendium of three papers, each dealing with a separate spacecraft that carried one or more instruments based on the electric probe technique.
The first paper presents data from the Sudden Atom Layer sounding rocket that carried an RF Impedance Probe, a DC fixed-bias Langmuir Probe (DCP), and an Electric Field Probe. The combined dataset indicates a case of payload surface charging, the causes of which are investigated within the paper. A generic circuit model is developed to analyze payload charging and behavior of Langmuir-type instruments. Our analysis indicates that the anomalous charging event was an outcome of triboelectrification of the payload surface from neutral dust particles present in the Earth’s mesosphere. These results suggest caution in interpreting observations from the Langmuir class of instrumentation within dusty environments.
The second paper presents data from the Floating Potential Measurement Unit (FPMU) that is deployed on the International Space Station. The FPMU instrument suite consists of three different Langmuir-type probes and a Plasma Impedance Probe (PIP). We first give a brief overview of the instrumentation, and then describe the algorithm used to reduce Langmuir probe I-V curves to plasma parameters. It is shown that the derived temperatures agree well with International Reference Ionosphere (IRI) model, while the derived density matches better with the USU-Global Assimilation of Ionospheric Measurement model. The third paper presents the dataset from the EQUIS II sounding rocket campaign. The rocket payloads carried a PIP, a DCP, and an internally heated Sweeping Langmuir Probe. The ratio of the payload surface area to the cumulative area of the instrument and its guard was about 250. We show that on small sounding rocket payloads the DCP technique of relative electron density measurement is not very accurate. We further show that the ion saturation region analysis of the I-V curve produces absolute ion density that matches very well with the absolute electron density derived from the PIP, and the derived temperatures agree reasonably well with the IRI model.
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Jacobi, Christoph, and Dierk Kürschner. "Interannual variability of the quasi two-day wave over Central Europe (52°N, 15°E)." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-223179.
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Using the spaced receiver method in the low-frequency (LF) range, lower E-region ionospheric drifts are measured at Collm Observatory, Germany since several decades. These drifts are interpreted as upper mesospheric winds at the reflection height of the used amplitude modulated LF radio waves, the latter being measured since 1983 using travel time differences between the ground wave and the ionospherically reflected sky wave within a small sideband range near 1.8 kHz above and below the carrier frequency. One regular feature of midlatitude upper mesosphere winds is the quasi twoday wave (QTDW), known as a wavenumber 3 or 4 wave in the middle atmosphere, usually occurring as one or more bursts during the summer season at midlatitudes. The OTDW bursts, as measured in LF winds, shows substantial decadal and interannual variability. Comparison with the background winds show that the onset of QDTW bursts is found near maximum values of the vertical wind shear, and maximum QTDW amplitudes are measured, on average, about one week after the maximum wind shear. This supports the theory that the QTDW is forced by instability of the summer mesospheric wind jetAm Observatorium Collm werden seit mehreren Jahrzehnten Langwellenwindmessungen in der unteren ionosphärischen E-Schicht durchgeführt. Die zugehörige Reflexionshöhe wird, auf der Basis von Laufzeitdifferenzmessungen zwischen der Raum- und Bodenwelle, seit 1983 ebenfalls registriert. Eines der regelmäßig beobachteten Phänomene ist die quasi 2-Tage-Welle, die als eine planetare Welle der Wellenzahl 3 oder 4 bekannt ist. Diese Welle erscheint in mittleren Breiten in einem oder mehreren Schüben im Sommer. Nach den Messungen am Collm besitzt die Welle eine deutliche Variabilität von Jahr zu Jahr. Vergleiche mit dem zonalen Grundwind zeigen, dass das Auftreten von Maxima der 2-Tage-Welle in vielen Fällen mit erhöhter vertikaler Windscherung in Verbindung steht, so dass im langzeitlichen Mittel maximale Wellenamplituden einige Tage nach dem Auftreten maximaler Windscherung zu finden sind. Dies unterstützt die These, dass die quasi 2-Tage-Welle durch barokline Instabilität des sommerlichen Mesosphärenjets angeregt wird
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Mbambo, Makhangela Casey. "Variability of the peak height of the ionospheric F2 layer over South Africa." Thesis, University of Fort Hare, 2011. http://hdl.handle.net/10353/446.
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Abstract This thesis will present an investigation into the variability of the maximum height of the ionospheric F2 layer, hmF2, with hour, season and latitude over the South African region. The dependence of hmF2 on solar and magnetic activity is also investigated. Data from three South African stations, namely Madimbo (22.4 S, 26.5 E), Grahamstown (33.3 S, 26.5 E) and Louisvale (28.5 S, 21.2 E) were used in this study. Initial results indicate that hmF2 shows a larger variability around midnight than during daytime for all the seasons. Monthly median values for hmF2 were used in all cases to illustrate the variability, and the International Reference Ionosphere (IRI) model has been used to investigate hmF2 predictability over South Africa. This research represents the initial steps towards a predictive model for the hmF2 parameter, with the long term aim of developing a new global hmF2 predictive model for the IRI. It is believed that this work will contribute signi cantly towards this aim through the understanding of the hmF2 parameter over a region that has not previously been investigated.
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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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Singh, Dupinder. "Study of ionospheric variabilities in the equatorial and low latitude region." Thesis, IIG, 2010. http://localhost:8080/xmlui/handle/123456789/1591.
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Jacobi, Christoph, and Dierk Kürschner. "Ergebnisse ionosphärischer Messungen am Observatorium Collm während der totalen Sonnenfinsternis vom 11. 8.1999." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-215460.
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Während der Sonnenfinsternis am 11. 8. 1999 kam es zu einer kurzzeitigen starken Abnahme der Ionisation im Höhenbereich der D-Region (60-90 km Höhe) am Unterrand der Ionosphäre. Mit bodengebundenen funktechnischen Beobachtungen der Ausbreitung elektromagnetischer Wellen über die D-Region konnte dieses Ereignis in charakteristischer Weise als ein simulierter Tag-Nacht-Übergang mit allen zu erwartenden Konsequenzen beobachtet werden. Auf der Basis von Funkwellen-Ausbreitungsmessungen werden in Collm (51.3°N, 13°E) Windmessungen im Höhenbereich der Mesopause und unteren Thermosphäre (80-105 km) durchgeführt, die in der Regel - bedingt durch die Besonderheiten der ionosphärischen Wellenausbreitung des verwendeten Frequenzbereiches - nur in den Nachtstunden möglich sind. Während der Hauptphase des Finsterniseffektes wurden Messungen auch am Tag möglich. Die Ergebnisse fügen sich gut in das aus den mittleren monatlichen Nachtwerten für die Tagstunden extrapolierte Niveau ein. Die Reaktion der Ionosphäre auf die Sonnenfinsternis erfolgte mit geringer Verzögerung: der maximale Effekt war 5-10 Minuten nach der größten Abdeckung der Sonnenscheibe zu verzeichnenDuring the solar eclipse on 11 August 1999 a short-term decrease of ionisation in the D-region ( 60- 90 km altitude) at the lower boundary of the ionosphere appeared. Using ground-based measurements of radio-wave propagation through the D-region the event could be monitored as a simulated day-night-transition with the expected consequences for the ionosphere. At Collm (51.3°N, 13°E), mesopause region (80-105 km) windmeasurements are carried out based on radio wave propagation, which are not possible in summer during daylight hours due to radio-wave absorption. During the eclipse measurements became possible for a short period. Tue results fit well to mean monthly daytime data extrapolated from nighttime measurements. The reaction of the ionosphere on the solar eclipse was fast; the maximum effect was registered only 5-10 minutes after the maximum eclipse of the solar disk
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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.
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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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Hekman, Thomas P. "Far ultraviolet images of the nighttime ionosphere." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA275083.
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Thesis (M.S. in Systems Engineering (Electronic Warfare)) Naval Postgraduate School, September 1993.Thesis advisor(s): David D. Cleary. "September 1993." Bibliography: p. 58. Also available online.
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Verronen, Pekka T. "Ionosphere-atmosphere interaction during solar proton events /." Helsinki : Finn. Meteorological Inst, 2006. http://www.gbv.de/dms/goettingen/520955706.pdf.
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Peters, Bevis Michael. "A Martian thermosphere : ionosphere general circulation model." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271688.
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Crowley, G. "Doppler radar studies of the Antarctic ionosphere." Thesis, University of Leicester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353168.
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Butler, Thomas W. "Spatial statistics and analysis of earth's ionosphere." Thesis, Boston University, 2013. https://hdl.handle.net/2144/10950.
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Thesis (Ph.D.)--Boston UniversityThe ionosphere, a layer of Earths upper atmosphere characterized by energetic charged particles, serves as a natural plasma laboratory and supplies proxy diagnostics of space weather drivers in the magnetosphere and the solar wind. The ionosphere is a highly dynamic medium, and the spatial structure of observed features (such as auroral light emissions, charge density, temperature, etc.) is rich with information when analyzed in the context of fluid, electromagnetic, and chemical models. Obtaining measurements with higher spatial and temporal resolution is clearly advantageous. For instance, measurements obtained with a new electronically-steerable incoherent scatter radar (ISR) present a unique space-time perspective compared to those of a dish-based ISR. However, there are unique ambiguities for this modality which must be carefully considered. The ISR target is stochastic, and the fidelity of fitted parameters (ionospheric densities and temperatures) requires integrated sampling, creating a tradeoff between measurement uncertainty and spatio-temporal resolution. Spatial statistics formalizes the relationship between spatially dispersed observations and the underlying process(es) they represent. A spatial process is regarded as a random field with its distribution structured (e.g., through a correlation function) such that data, sampled over a spatial domain, support inference or prediction of the process. Quantification of uncertainty, an important component of scientific data analysis, is a core value of spatial statistics. This research applies the formalism of spatial statistics to the analysis of Earth's ionosphere using remote sensing diagnostics. In the first part, we consider the problem of volumetric imaging using phased-array ISR based on optimal spatial prediction ("kriging"). In the second part, we develop a technique for reconstructing two-dimensional ion flow fields from line-of-sight projections using Tikhonov regularization. In the third part, we adapt our spatial statistical approach to global ionospheric imaging using total electron content (TEC) measurements derived from navigation satellite signals.
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Gavrilov, Nikolaj M., Christoph Jacobi, and Dierk Kürschner. "Drifts and their short-period perturbations in the lower ionosphere observed at Collm during 1983 - 1999." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 17 = Meteorologische Arbeiten aus Leipzig ; 5 (2000), S. 74-87, 2000. https://ul.qucosa.de/id/qucosa%3A15150.
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Estimations of the intensity of short-period perturbations of the horizontal drift velocity at 80 - 110 km altitude are made using data from the regular low-frequency D1 ionospheric reflection observations at Collm, Germany (52° N, 15° E) for the period 1983 - 1999. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales between 0.7 and 3 hours. The results are compared with the mean drift analyses in order to study the interaction between short-period perturbations and the mean circulation. The average monthly variances of short-period perturbations of the zonal velocity near 80 km altitude show a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards spring, and another maximum of perturbation variances in autumn appears at altitudes near and above 100 km. The seasonal changes of variances of the meridional velocity show maximum values in spring and summer, also some indications for an increase of the summer maximum at altitudes larger than 100 km are found. The observed altitude changes of the seasonal variations of drift perturbation variances are consistent with some numerical calculations of the height structure of a spectrum of internal gravity waves in the middle and upper atmosphere.Die Intensität kurzperiodischer Störungen der horizontalen Driftgeschwindigkeit im Höhenbereich zwischen 80 und 110 km wurde anhand der regulären D1 Langwellenreflexionsmessungen in Collm (52° N, 15° E), bestimmt. Verwendet wurden Daten der Jahre 1983 - 1999. Ein einfache numerische Filter basierend auf den Unterschieden aufeinanderfolgender halbstündiger Windmittelwerte wurde verwendet, um Störungen im Zeitbereich von 0.7 - 3 Stunden zu ermitteln. Die Ergebnisse wurden mit Analysen der mittleren Drift verglichen, um die Wechselwirkungen zwischen kurzperiodischen Störungen und der mittleren Zirkulation zu untersuchen. Die mittlere monatliche Varianz der kurzperiodischen Störungen der Zonalgeschwindigkeit bei etwa 80 km zeigt ein Hauptmaximum im Sommer und ein schwächeres Maximum im Winter, wobei die Minima während der Aquinoktien auftreten. In grösseren Höhen verschiebt sich das Sommermaximum zum Frühjahr hin, und in Höhen über 100 km erscheint im Herbst ein weiteres Maximum. Der Jahresgang der meridionalen Windstörungen zeigt maximale Werte in Frühjahr/Sommer, und es sind auch Hinweise auf eine Verstärkung des Sommermaximums oberhalb von 100 km zu finden. Die gemessenen Höhenänderungen im Jahresgang der kurzperiodischen Driftschwankungen entsprechen numerischen Ergebnissen der Höhenabhängigkeit interner Schwerewellen in der mittleren und oberen Atmosphäre.
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Pitkänen, T. (Timo). "Dynamics of the polar cap boundary and the auroral oval in the nightside ionosphere." Doctoral thesis, University of Oulu, 2011. http://urn.fi/urn:isbn:9789514294471.
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Abstract
The high-latitude polar ionosphere is characterized by two regions, the polar cap and the auroral oval. In the polar cap, the geomagnetic field lines are open and connect to the solar wind, whereas the field lines in the auroral oval are closed and map to the plasma sheet and the plasma sheet boundary layer in the magnetosphere. The two substantially different magnetic and plasma domains are separated by a separatrix, the polar cap boundary (PCB), which is an ionospheric projection of the open-closed field line boundary (OCB) in the magnetosphere.
In this thesis, a new method to determine the location of the PCB in the nightside ionosphere based on electron temperature measurements by EISCAT incoherent scatter radars is introduced. Comparisons with other PCB proxies like poleward boundary of the auroral emissions, poleward edge of the auroral electrojets and poleward boundary of energetic particle precipitation show general agreement. By applying the method to several events together with other supporting ground-based and space-borne observations, dynamic processes and phenomena in the vicinity of the PCB and inside the auroral oval are studied.
The main results include the following. During substorm expansion, the PCB moves poleward in a burstlike manner with individual bursts separated by 2–10 min, indicating impulsive reconnection in the magnetotail. In one event, a possible signature of the high-altitude counterpart of the Earthward flowing field-aligned current of the Hall current system at the magnetotail reconnection site is observed. Investigation of the relation between the auroral activity and the local reconnection rate estimated from the EISCAT measurements reveals direct association between individual auroral poleward boundary intensifications (PBIs) and intensifications in the ionospheric reconnection electric field within the same MLT sector. The result confirms earlier suggestions of positive correlation between PBIs and enhanced flux closure in the magnetotail. In another event, quiet-time bursty bulk flows (BBFs) and their ionospheric signatures are studied. The BBFs are found to be consistent with the so called "bubble" model with Earthward fast flows inside the region of depleted plasma density (bubble). The tailward return flows show an interesting asymmetry in plasma density. Whereas the duskside return flows show signatures of a depleted wake, consistent with a recent suggestion, no similar feature is seen for the dawnside return flows, but rather increase in density. The BBFs are associated with auroral streamers in the conjugate ionosphere, consistently with previous findings. The related ionospheric plasma flow patterns are interpreted as ionospheric counterpart of the BBF flows, excluding the dawnside return flows which could not be identified in the ionosphere. The BBFs and streamers are found to appear during an enhanced reconnection electric field in the magnetotail.
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Shytermeja, Enik. "Design and performance of a GNSS single-frequency multi-constellation vector tracking architecture for urban environments." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19756/1/SHYTERMEJA_Enik.pdf.
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In the last decade, Global Navigation Satellites Systems (GNSS) have gained a significant position in the development of urban navigation applications and associated services. The urban environment presents several challenges to GNSS signal reception, such as multipath and GNSS Line-of-Sight (LOS) blockage, which are translated in the positioning domain in a decreased navigation solution accuracy up to the lack of an available position. For this matter, Vector Tracking (VT) constitutes a promising approach able to cope with the urban environment-induced effects including multipath, NLOS reception and signal outages. This thesis is particularly focused on the proposal and design of a dual constellation GPS + Galileo single frequency L1/E1 Vector Delay Frequency Lock Loop (VDFLL) architecture for the automotive usage in urban environment. From the navigation point of view, VDFLL represents a concrete application of information fusion, since all the satellite tracking channels are jointly tracked and controlled by the common navigation Extended Kalman filter (EKF). The choice of the dual-constellation single frequency vector tracking architecture ensures an increased number of observations and at the same time allowing the conservation of the low-cost feasibility criteria of the mobile user’s receiver. Moreover, the use of single frequency L1 band signals implies the necessity of taking into account the ionospheric error effect. In fact, even after the application of the ionosphere error correction models, a resultant ionospheric residual error still remains in the received observations. The originality of this work relies on the implementation of a dual-constellation VDFLL architecture, capable of estimating the ionosphere residual error present in the received observations. This dissertation investigates the VDFLL superiority w.r.t the scalar tracking receiver in terms of positioning performance and tracking robustness for a real car trajectory in urban area in the presence of multipath and ionosphere residual error.
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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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Stolle, Claudia, Christoph Jacobi, Norbert Jakowski, Stefan Schlüter, and Armin Raabe. "Comparison of electron density profiles in the ionosphere from ionospheric assimilations of GPS, CHAMP profiling and ionosondes over Europe." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-218294.
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GPS integrated Total Electron Content measurements received at the ground or in space are used for tomographic reconstruction of the ionospheric electron density distribution. The IRI/GCPM model is used as initialisation of the tomographic MART algorithm. During the procedure GPS TEC data are iteratively assimilated to the model. To test the potential of the reconstruction, electron density profiles from IRI/GCPM and the assimilation are compared with ionosonde measurements and CHAMP radio occultation profiles for dates during the HIRAC campaign in April 2001. All profiling methods show electron density values of similar magnitude. It is shown that including TEC GPS data corrects the model towards the ionosonde measurementsIntegrale Messungen der Elektronendichte aus GPS-Boden- sowie Radio-Okkultations-Messungen bilden die Datenbasis der hier vorgestellten 3-dimensionalen Tomographie der ionosphärischen Elektronendichteverteilung. Zur Initialisierung des verwendeten iterativen MART Algorithmus wird das IRI/GCPM Modell verwendet, wobei das Modell während der Iteration sukzessiv an die Messdaten angepasst wird. Um das Potential des Verfahrens abzuschätzen, werden Elektronendichteprofile des IRI/GCPM Modells und der Rekonstruktion mit Ionosondenmessungen und CHAMP Okkultationsprofilen verglichen. Dafür wurden Messungen während der HIRAC Kampagne im April 2001 genutzt. Alle hier gezeigten Profilableitungen geben Elektronendichtewerte der selben Größe wieder. Eine Annäherung des IRI/GCPM Modells an die Messwerte der Ionosonde durch die Assimilation der TEC GPS Daten wird gezeigt
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Stolle, Claudia, Stefan Schlüter, Christoph Jacobi, and Norbert Jakowski. "Ionospheric tomography and first interpretations of including space-based GPS." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217058.
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When L-band radio waves of space-based radio navigation systems such as Global Positioning System (GPS) travel through the atmosphere and ionosphere, their ray paths are bent and their travel time are increased as a result of refractive-index gradients. As the ionosphere is a dispersive medium the two GPS frequencies are subject to different delays in time and modifications in amplitude, phase and polarisation which is an effect of free electrons. By using these two radio frequencies one can derive information about the Total Electron Content integrated along the ray path. After calibration, these data are included into the tomographic reconstruction. The tomographic methode presented in this paper works on algebraic iterative methodes like SART and MART. Calculations are based on International GPS Service (IGS) ground received data. Space-based GPS is provided by LEO (Low Earth Orbiter) satellites like CHAMP. By means of incorporating such occultation data into tomography an improvement of reconstruction of the vertical structure of the electron density is expected. First confirming interpretations of a selected occulation event are presented in this paper. It is shown, that space-based GPS data can improve tomographic results mainly in middle to lower altitudes of the ionosphereWenn sich Radiowellen eines Navigationssystemes, wie das des Global Positioning Systems (GPS), in der Atmosphäre und Ionosphäre ausbreiten, erfahren sie eine Beugung des Strahlweges und eine Erhöhung der Laufzeit aufgrund der Gradienten des atmosphärischen Refraktionsindexes. Da die Ionosphäre ein dispersives Medium darstellt, unterliegen beide GPS-Frequenzen dort unterschiedlichen Störungen in Laufzeit und Veränderungen in Amplitude, Phase und Polarisation, was auf die Effekt der freien Elektronen zurückzuführen ist. Unter der Verwendung der beiden Radiofrequenzen kann man Informationen über die Anzahl der über den Strahlweg integrierten Elektronen erhalten. Nach der Kalibrierung dieser Daten, können sie zur tomographischen Rekonstruktion verwendet werden. Die hier vorgestellte Tomographie verwendet algebraisch iterative Methoden, wie SART und MART. Die tomographischen Berechnungen bauen auf bodengestützte GPS-Daten des International GPS Services (IGS) und satellitengestützten GPS-Daten von LEO (Low earth orbiter) Satelliten wie CHAMP auf. Durch die Intergration von Okkultationsdaten in die Tomographie wird eine Verbesserung der Rekonstruktion der vertikalen Struktur der Elektronendichte erwartet. Erste bestätigende Interpretationen eines ausgewählten Okkultationsereignisses werden in diesem Artikel vorgeführt. Es wird gezeigt, dass satellitengestützte GPS-Daten die tomographischen Ergebnisse vorallem in der mittleren und unteren Ionosphäre verbessern können
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Stolle, Claudia, Stefan Schlüter, Christoph Jacobi, Norbert Jakowski, and Armin Raabe. "Monitoring of a polar plasma convection event with GPS." Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 30 = Meteorologische Arbeiten aus Leipzig ; 8 (2003), S. 112-120, 2003. https://ul.qucosa.de/id/qucosa%3A15240.
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When L-band radio waves of space based systems such as Global Positioning System (GPS) travel trough the ionosphere and plasmasphere their ray paths are perturbed due to the free electrons. Since the last decade these integrated measurements are used to map the ionosphere for navigational and scientific investigations. In November 2001 a polar plasma convection like ionospheric event has been recognised in vertical TEC maps produced with GPS data. This event on the one hand is shortly compared with the behaviour of the Interplanetary Magnetic Field (IMF) to which it may be related according to former publications. On the other hand the 3-dimensional tomography applying also GPS data is tested on its capability to reconstruct this ionospheric event in the European sector. The different mappings of the two monitoring methods are compared.Wenn L-Band-Radiowellen raumgestützter Navigationssysteme wie das Global Positioning System (GPS) die Ionosphäre oder Plasmasphäre durchlaufen, werden Ihre Strahlwege durch die freien Elektronen verändert. Seit dem letzten Jahrzehnt verwendet man diese integrierten Messungen, um die Ionosphäre im Interesse der Navigation und der Wissenschaft abzubilden. Am Beispiel eines Ereignisses vom November 2001 wurde eine polare Plasmakonvektion in der Ionosphäre durch vertikale TEC –Karten (Total Electron Content), die ebenfalls mit Hilfe von GPS Daten erstellt werden, abgebildet. Einerseits wurde das Ereignis der Plasmakonvektion mit dem Verhalten des Interplanetaren Magnetischen Feldes (IMF) kurz verglichen und auf ihren Zusammenhang hin untersucht. Auf der anderen Seite wurde anhand dieses Ereignisses die Methode einer über den europäischen Raum aufgespannten auf GPS–Daten basierenden 3-dimensionale Tomographie auf ihre Reproduzierbarkeit hin geprüft. Die zwei verschiedenen Methoden des Ionosphärenmonitorings werden verglichen.
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Okoh, Daniel Izuikeninachi. "Developing an ionospheric map for South Africa." Thesis, Rhodes University, 2009. http://hdl.handle.net/10962/d1005244.
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This thesis describes the development of an ionospheric map for the South African region using the current available resources. The International Reference Ionosphere (IRI) model, the South African Bottomside Ionospheric Model (SABIM), and measurements from ionosondes in the South African Ionosonde Network, were incorporated into the map. An accurate ionospheric map depicting the foF2 and hmF2 parameters as well as electron density profiles at any location within South Africa is a useful tool for, amongst others, High Frequency (HF) communicators and space weather centers. A major product of the work is software, written in MATLAB, which produces spatial and temporal representations of the South African ionosphere. The map was validated and demonstrated for practical application, since a significant aim of the project was to make the map as applicable as possible. It is hoped that the map will find immense application in HF radio communication industries, research industries, aviation industries, and other industries that make use of Earth-Space systems. A potential user of the map is GrinTek Ewation (GEW) who is currently evaluating it for their purposes
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Edwards, Thomas Raymond. "Empirical Ionospheric Models: The Road To Conductivity." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100284.
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The Earth's polar ionosphere is a highly dynamic region of the upper atmosphere, and acts as the closure of the greater magnetospheric current system. This region plays host to many electrodynamic effects that impact terrestrial systems, such as power grids, railroads, and pipelines. These effects are fundamentally related to the currents, electric fields, and conductivity present in the polar ionosphere. Understanding and predicting the electrodynamics of this region is vital to being able to determine the physical impacts on terrestrial systems and provide predictions to government and commercial entities.
Empirical models play a key role in the research and forecasting of the solar wind and interplanetary magnetic field's impact on the polar ionosphere, and is an active area of development and research. Recent interest in polar ionospheric conductivity has led to a community-wide campaign to develop our understanding of this portion of the electrodynamic system.
Characterizing the interactions between the solar wind and the polar ionosphere is a difficult task, as the region of interest is highly data starved in many respects. In particular, satellite based data products are scarce due to being costly and logistically difficult. Recent advancements in data sources (such as the Swarm and CHAMP satellite missions) as well as continued research into the physical relationships between solar wind and interplanetary magnetic field drivers have provided the opportunity to develop new, novel tools to study this region of interest. In this dissertation, two polar ionosphere models are described in Chapters 3 and 4, along with the original research that their construction has produced in Chapter 1. These two models are combined to provide a foundation for future research in this area, which is described in Chapter 5.Doctor of Philosophy
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Sibanda, Patrick. "Particle precipitation effects on the South African ionosphere." Thesis, Rhodes University, 2007. http://hdl.handle.net/10962/d1005267.
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Particle precipitation involves the injection of energetic particles into the ionosphere which could increase the ionisation and conductivity of the upper atmosphere. The goal of this study was to examine the ionospheric response and changes due to particle precipitation in the region over South Africa, using a combination of groundbased and satellite instruments. Particle precipitation events were identified from satellite particle flux measurements of the Defence Meteorological Satellite Program (DMSP). Comprehensive studies were done on the events of 5 April, 2000 and 7 October, 2000. Analysis of the data from the satellite instruments indicates that no particle precipitation was observed over the South African region during these events and that it is unlikely to occur during other such events. To validate the data, methods and tools used in this study, precipitation in the South Atlantic anomaly (SAA) region is used. Satellite ion density measurements revealed that strong density enhancements occurred over the SAA region at satellite altitudes during the precipitation events, but this did not occur in the South African region. The measurements also revealed how the ionisation enhancements in the SAA region correlated with geomagnetic and solar activities. Particle precipitation and convective electric fields are two major magnetospheric energy sources to the upper atmosphere in the auroral and the SAA regions. These increase dramatically during geomagnetic storms and can disturb thermospheric circulation in the atmosphere and alter the rates of production and recombination of the ionised species. Ionosonde observations at Grahamstown, South Africa (33.30S, 26.50E), provided the data to build a picture of the response of the ionosphere over the South African region to particle precipitation during the precipitation events. This analysis showed that, within the confines of the available data, no direct connections between particle precipitation events and disturbances in the ionosphere over this region were revealed.
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Wild, James. "Electrodynamics of the auroral ionosphere during magnetospheric substorms." Thesis, University of Leicester, 2000. http://hdl.handle.net/2381/30641.
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One of the principal consequences of magnetic reconnection at the dayside magentopause is the transfer of solar wind energy in the Earth's magnetotail. The expansion phase of a magnetospheric substorm corresponds to the sudden release of this energy and is characterised in the ionosphere by the sudden brightening and poleward expansion of the auroral oval near midnight and the intensification of the ionospheric currents flowing in the auroral zone. Observations of various high-latitude ionospheric phenomena associated with magnetospheric substorm are presented. In particular, use is made of the Co-operative UK Twin Located Auroral Sounding System (CUTLASS), a high frequency bistatic coherent-scatter radar with sites in Finland and Iceland. Azimuthally Propagating Vortical Currents (APVCs) are the ionospheric flow signatures of upward directed field-aligned currents in the nightside ionosphere. Two case studies of APVCs are presented and their structure examined in detail. In addition, the results of a statistical study of APVC occurrence encompassing over 1000 hours of high-time resolution data are discussed with particular focus on the relationship of APVCs to magnetospheric substorm phase. Omega bands are a distinct class of auroral form that have previously been observed in the morning sector during the recovery phase of magnetospheric substorms. High-time resolution measurements of the ionospheric flow within a series of omega bands from the CUTLASS Finland radar are presented. Complementary observations from the Scandinavian Twin Auroral Radar Experiment (STARE) and ground magnetometers of the IMAGE array are employed in order to characterise the electric and magnetic field structure of omega bands. Revised descriptions of omega band structure and formation mechanism are proposed. Finally, multi-instrument observations of the evolution of a high-latitude polar auroral arc during the recovery phase of an isolated substorm are presented and its relation to upstream interplanetary magnetic field conditions discussed.
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Wild, Paul. "Dynamics of particle precipitation in the auroral ionosphere." Thesis, Lancaster University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.654965.
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Talaee, Omid. "Distribution of Electron Temperatures in Titan's Lower Ionosphere." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-194685.
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The report contained herein is a statistical analysis of electron temperatures withinTitan’s lower ionosphere. Electron temperatures in this altitudinal range are of greatimport for researchers. The main contributing factors are investigated to see whatphysical processes are the sources of variability in electron temperatures. Oneimportant result from this analysis lends itself to determining recombinationcoefficients thus determining organic process rates occurring within Titan’satmosphere. To accomplish this analysis, data from the Langmuir probe aboard the Cassini craft isutilized. The Langmuir probe is an instrument which can be used to measure currentdifferences in a plasma environment. From this, plasma properties such astemperature, density, and velocity can be calculated. It was named after IrvingLangmuir, whose theories became the basis for Orbit Motion Limited theory. Of the possible factors that determine the variation in electron temperatures, altitudewas the most evident and largest contributor. Once the data had been reduced toremove the effect of altitude on the temperature, other factors such as latitude, solarzenith angle, and ram angle were investigated to ascertain which, if any, wasresponsible for variations in temperature. Upon completion of the analysis, it waslearned that ram angle also had an identifiable effect upon electron temperatures. This effect was further investigated to ensure confidence in the results. Thecompletion of this part of the analysis showed that the effect shown with respect toram angle was indeed reproducible and that no other investigated factor had a majoreffect on electron temperatures. After the confidence procedure was completed,several previous studies findings were confirmed. These confirmed results include therelation of solar zenith angle with respect to both electron temperature distributionand density distribution, as well as a possible confirmation relating temperature anddensity for electrons.n/
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Davies, Jacqueline Anne. "Ion frictional heating in the high-latitude ionosphere." Thesis, University of Leicester, 1996. http://hdl.handle.net/2381/35864.
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At auroral latitudes, large electric fields drive the F-region plasma of the ionosphere through the thermosphere, heating the ion population through frictional contact with the neutral gas. Ion frictional heating, which can double the unperturbed ion temperature, is an important manifestation of both magnetosphere-ionosphere and ionosphere-thermosphere interaction and provides a significant contribution to the energy budget of the ionosphere and neutral atmosphere at high-latitudes. Perhaps the single most powerful technique for ground based remote sensing of the ionosphere is incoherent scatter. The EISCAT radar facility, located in northern Scandinavia, employs this technique to investigate the highly dynamic nature of the high-latitude ionosphere. This thesis documents a study of ion frictional heating in the high-latitude ionosphere, principally employing common programme observations by the tristatic EISCAT UHF system. In excess of 3200 hours of EISCAT observations, taken during a six year period, were employed to study, on a statistical basis, ion frictional heating in the high-latitude F-region. The diurnal distribution of frictional heating was established and its dependence on such factors as geomagnetic activity and solar cycle was investigated; the distributions were interpreted with reference to corresponding distributions of enhanced ion velocity. A prolonged and intense interval of ion frictional heating was observed by EISCAT postnoon on 04/03/1992: this interval was modelled, using the Sheffield University plasmasphere and ionosphere model, and the model results compared with the observations. This study highlights the importance of ionospheric effects in determining neutral dynamics, particularly on the dayside. Furthermore, during this interval, the altitude dependence of the effect of enhanced electric fields on the velocity and temperature of the ion population was studied and, moreover, employed to provide first-order estimates of the normalised ion-neutral collision frequency and the neutral wind at E-region altitudes.
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Nichols, Jonathan D. "Magnetosphere-ionosphere coupling currents in Jupiter's middle magnetosphere." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/30679.
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This thesis is a theoretical study of the magnetosphere-ionosphere coupling current system in Jupiter's middle magnetosphere associated with the breakdown of corotation of iogenic plasma and the jovian main auroral oval. The study initially investigates the effects of the ionospheric Pedersen conductivity and the iogenic plasma mass outflow rate. Wide ranges of values of these parameters are inputted to the model and the results are compared for dipole and current sheet field models. It is shown that previous results, obtained using 'reasonable' spot values, are generally valid over wide ranges of the parameters. The study then investigates the effect of precipitation-induced enhancements of the Pedersen conductivity. Previous models have assumed constant conductivity, whereas it is expected to be significantly elevated by strong field-aligned currents. A model of the dependence of the Pedersen conductivity on the field-aligned current is developed and incorporated into the model. The findings help reconcile the theoretical results with observation. Specifically, the plasma is maintained closer to rigid corotation out to much further distances than theory previously predicted, the equatorial radial current exhibits a sharp rise in the inner region of the middle magnetosphere and plateaus off thereafter, in line with Galileo magnetic field data, and the field-aligned current is concentrated in a peak in the inner region, which is to where the main oval is usually mapped. Finally, the study investigates the effect of self-consistently including magnetosphere-ionosphere decoupling due to field-aligned voltages. The results show that for typical jovian conditions the effect is very small, such that the modification to the system parameters is generally two orders of magnitude below the values of the parameters themselves. The conclusion is that the assumption made in previous work, that the effect of the field-aligned voltages is small, is generally valid.
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Wilder, Frederick Durand. "Reverse Convection Potential Saturation in the Polar Ionosphere." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/31847.
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The results of an investigation of the reverse convection potentials in the day side high latitude ionosphere during periods of steady northward interplanetary magnetic field (IMF) are reported. While it has been shown that the polar cap potential in the ionosphere exhibits non-linear saturation behavior when the IMF becomes increasingly southward, it has yet to be shown whether the high latitude reverse convection cells in response to increasingly northward IMF exhibit similar behavior. Solar wind data from the ACE satellite from 1998 to 2005 was used to search for events in the solar wind when the IMF is northward and the interplanetary electric field is stable for more than 40 minutes. Bin-averaged SuperDARN convection data was used with a spherical harmonic fit applied to calculate the average potential pattern for each northward IMF bin. Results show that the reverse convection cells do, in fact, exhibit non-linear saturation behavior. The saturation potential is approximately 20 kV and is achieved when the electric coupling function reaches between 18 and 30 kV/RE.Master of Science
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Mao, Xiaolei. "GPS CARRIER SIGNAL PARAMETERS ESTIMATION UNDER IONOSPHERE SCINTILLATION." Miami University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=miami1314295002.
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Wang, Jun. "SPECTRAL CHARACTERIZATION OF IONOSPHERE SCINTILLATION: ALGORITHMS AND APPLICATIONS." Miami University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=miami1385774581.
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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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Nayak, Chinmaya Kumar. "Study of the variability of equatorial and low latitude ionosphere in the Indian region using radio waves." Thesis, Indian Institute of Geomagnetism, Mumbai, 2013. http://localhost:8080/xmlui/handle/123456789/215.
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A thesis submitted to the University of Mumbai for the Ph.D (Science) Degree in Physics under the guidance of Dr. Satyavir Singh.This thesis addresses three different aspects of the equatorial ionosphere during a period of extended solar minimum (2007-2009). Chapter I gives a detailed introduction to various features of the equatorial ionosphere while the chapters II, III, and IV discusses the work done during the course of this thesis. In this chapter, the summary and conclusions of the research work presented in the thesis have been discussed, with the scope for the future investigations.The occurrence of F3-layer over the equatorial station Tirunelveli during the pro longed lower solar activity period 2007-2009 is discussed in detail in chapter II. A clear diurnal and seasonal dependence of the occurrence of F3-layer has been estab lished in this study. Earlier studies show that the occurrence of F3-layer is favored during local summer months (May, June, July) as compared to winter and equinoxes. The results from this study indicate that the F3-layer is equally probable during equinoctial months (March, April, September and October) as compared to summer months (May, June and July). However it is least probable during local winter months ( November, December, January, February).The present understanding suggests that the formation of F3-layer is due to the com bined action of vertically upward E×B drift and the equatorward neutral wind [Balan et al.,1998]. The pre noon period F3-layer observations support this theory. In most of the cases, the F3-layer is found to occur at a time when the EEJ attains its peak of the day. This represents the fact that the zonal electric field is eastward and hence the E × B is vertically upward and increasing so that the plasma moves upward fast enough to create a new layer at the lower heights resulting in three different layers; F1-. F2- and F3-layer. A clear dependence of F3-layer occurrence over the variation of EEJ has been discussed in chapter II. The formation of F3-layer is mainly attributed to the vertically upward E × B drift, which moves the F-layer plasma upwards in altitude. However, our study brings out the afternoon time occurrence of F3 layer, which may be associated with downward movement of F-layer plasma. This possibility gets strengthened due to the fact that all such happen during the presence of a counterelectrojet (CEEJ) , which can be used as a proxy for zonal electric field. Some such cases have been discussed in chap ter II. Modeling efforts are necessary to understand the physical process linked with these afternoon time occurrence of F3. Similarly, the absence of post sunset F3-layer at Tirunelveli is puzzling as this has been a common feature at other longitudes. A separate study may be undertaken to establish the reason behind this nonoccurrence.