The behaviour of the ionosphere during a solar eclipse is of great interest because radiation from the sun is the cause of ionization in the upper atmosphere and it is useful to be able to conduct experiments where this radiation is cut off and restored in a known manner. Experimental results, especially those dealing with the F2 layer, have proved puzzling. Cusps which cannot be explained appear on the records obtained from ionosphere sounders and in the F2 region the electron density at a given height shows a maximum after the eclipse where one would expect it simply to rise to a steady value. An attempt is made in this thesis to explain some of the anomalies in terms of tilts in the ionospheric layers and minima of electron density or "valleys" between the ionospheric layers. The problem is attacked theoretically. Part I deals with the theoretical background to ionospheric physics in general and to this problem in particular. Standard methods of dealing with radio propagation in the ionosphere as well as some methods developed by the author are discussed. Part II deals directly with the effects of a solar eclipse on a theoretical ionosphere. Ionograms which would be obtained in the theoretical ionosphere are constructed. These are scaled by standard methods to show where errors may arise . It appears that tilts in the layers have only a small effect. The effect of the valley is, however, extremely important, giving rise to the apparent maximum of electron density in the F2 layer at a given height after the eclipse. This maximum does not in fact exist but arises from an error in the scaling method which ignores the possibility of a valley. Some records taken during the solar eclipse of 25 December, 1954 have been scaled. They support the conclusion reached theoretically.

Abstract This dissertation presents new incoherent scatter radar measurement techniques and data analysis methods. The measurements used in the study were collected by connecting a computer-based receiver to the EISCAT (European Incoherent SCATter) radar on Svalbard. This hardware consists of a spectrum analyzer, a PCI-bus-based programmable digital I/O card and a desktop computer with a large-capacity hard disk. It takes in the 70-MHz signal from the ESR (Eiscat Svalbard Radar) signal path and carries out down-conversion, AD conversion, quadrature detection, and finally stores the output samples effective sampling rate is 1 MHz, large enough to span all the frequency channels used in the experiment. Hence the total multichannel signal was stored instead of separate lagged products for each frequency channel, which is the procedure in the standard hardware. This solution has some benefits including elimination of ground clutter with only a small loss in statistical accuracy. The capability of our hardware in storing the incoherent scatter radar signals directly allows us to use very flexible and versatile signal processing methods, which include clutter suppression, filtering, decoding, lag prole calculation, inversion and optimal height integration. The performance of these incoherent scatter radar measurement techniques and data analysis methods are demonstrated by employing an incoherent scatter experiment that applies a new binary phase code. Each bit of this code has been further coded by a 5-bit Barker code. In the analysis, stochastic inversion has been used for the first time in decoding Barker-coded incoherent scatter measurements, and this method takes care of the ambiguity problems associated with the measurements. Finally, we present new binary phase codes with corresponding sidelobe-free decoding filters that maximize the signal-to-noise ratio (SNR) and at the same time eliminate unwanted sidelobes completely. / Original papers The original papers are not included in the electronic version of the dissertation. Lehtinen, M., Markkanen, J., Väänänen, A., Huuskonen, A., Damtie, B., Nygrén, T., & Rahkola, J. (2002). A new incoherent scatter technique in the EISCAT Svalbard Radar. Radio Science, 37(4), 3-1-3–14. https://doi.org/10.1029/2001rs002518 Damtie, B., Nygrén, T., Lehtinen, M. S., & Huuskonen, A. (2002). High resolution observations of sporadic-E layers within the polar cap ionosphere using a new incoherent scatter radar experiment. Annales Geophysicae, 20(9), 1429–1438. https://doi.org/10.5194/angeo-20-1429-2002 Damtie, B., Lehtinen, M. S., & Nygrén, T. (2004). Decoding of Barker-coded incoherent scatter measurements by means of mathematical inversion. Annales Geophysicae, 22(1), 3–13. https://doi.org/10.5194/angeo-22-3-2004 Lehtinen, M. S., Damtie, B., & Nygrén, T. (2004). Optimal binary phase codes and sidelobe-free decoding filters with application to incoherent scatter radar. Annales Geophysicae, 22(5), 1623–1632. https://doi.org/10.5194/angeo-22-1623-2004

Total electron content (TEC) data measured from ground-based GPS receivers is compared to HF backscatter from ionospheric irregularities obtained by Super Dual Auroral Radar Network (SuperDARN) radars.  We present the first observations of a recurrent region of anomalous enhanced TEC at mid-latitudes over North America and attempt to characterize its frequency of occurrence.  Next, we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization (TOI) from mid-latitude plumes of storm enhanced density (SED) during a geomagnetic storm on 26 September 2011.  A channel of high density F region plasma was transported from the dayside ionosphere and into the polar cap by enhanced convection electric fields extending to mid-latitudes.  After the solar wind IMF conditions quieted and the dayside convection electric fields retreated to higher latitudes, an SED was observed extending to, but not entering, the dayside cusp region.  The source mechanism (enhanced electric fields) previously drawing the plasma from mid-latitudes and into the polar cap was no longer active, resulting in a fossil feature which persisted for several hours as it elongated in magnetic local time. Finally, we discuss ground surface effects on the HF backscatter observed by four SuperDARN radars. Monthly ground scatter occurrence rates are calculated for comparison with Arctic sea ice boundaries derived from satellite observations, showing reduced backscatter from regions covered by ice. / Master of Science

First time ionospheric refractive index values have been determined at mid latitudes using frequency switched SuperDARN plasma convection velocity estimates. Previous works have found a disparity between high latitude SuperDARN plasma convection velocities and those made by other devices. It was noted that the scattering volume’s refractive index was being neglected when estimating plasma convection velocities, meaning a correction factor was needed in order to more accurately reflect other measurements. Later work proposed a solution which implemented frequency switching in SuperDARN radars and determined a single correction factor based off of many years of data. We present case study driven research which applies the principles of these previous works to mid latitudes in an attempt to determine the refractive effect in mid latitude SuperDARN plasma convection velocity data by examining frequency switched quiet time ionospheric scatter. It was found that the 1/2 hop ionospheric scatter exhibited little to no measurable refractive effect (n ∼ 1), while the 11/2 hop ionospheric scatter tended to exhibit measurable refractive effects (n ∼ 0.7). This is then expanded to a storm-time 1/2 hop ionospheric scatter case study. It was again found that the refractive effects were nearly negligible (n ∼ 1), indicating that the 1/2 hop plasma convection velocities reported by mid latitude SuperDARN radars only require a very small correction factor, if any at all. / Master of Science

Ionospheric convection dynamics is an important window for understanding the coupling of the solar wind and interplanetary magnetic field to the Earth's ionosphere and upper atmosphere. In this study, we use measurements of ionospheric convection made by the SuperDARN radars to investigate the role of interhemispheric magnetic conjugacy in magnetosphere-ionosphere coupling and study the large-scale interactions between the magnetosphere and ionosphere. SuperDARN radars cover large geographic regions in both hemispheres and have a dataset spanning more than a decade, making them ideal for such studies. We begin in chapter 2 with an analysis of the degree of interhemispheric conjugacy exhibited in a Sub-Auroral Polarization Stream (SAPS). We present simultaneous observations of a SAPS event in both hemispheres made by mid-latitude SuperDARN radars with magnetically conjugate fields-of-view. An interhemispheric comparison of the characteristics of the SAPS channel reveals that the channel was conjugate in terms of potential variations across the channel even though substantial differences in latitudinal width and electric fields were observed in the channel. In chapter 3, we use interhemispheric SuperDARN observations of high latitude ionospheric convection in the noon-dusk sector to investigate the effects of IMF By penetrating into the closed magnetic field line region. The observations support the existence of an IMF By associated interhemispheric potential difference and field-aligned current system resulting in the generation of the interhemispheric asymmetries in ionospheric convection. Four events are analyzed in this study and the strength of interhemispheric currents associated with IMF By are estimated. Moreover, the strength of the interhemispheric currents is found to depend on the magnitude of IMF By, proximity of the currents to open-closed field line boundary, ionospheric conductivity and magnetic local time. In chapter 4, we use data from the mid-latitude SuperDARN radars between Jan-2011 and Aug-2012 to compile a database of SAPS events spanning about six hours in magnetic local time. The event database is used to analyze the average spatial variations in the occurrence rate and velocities of the SAPS channel under different geomagnetic conditions. An empirical model based on Dst-index is then developed to estimate the occurrence rate of SAPS at a given latitude and magnetic local time. / Ph. D.

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.

The DPS-4D is the latest version of digital ionosonde developed by the UMLCAR (University of Massachusetts in Lowell Center for Atmospheric Research) in 2008. This new ionosonde has advances in both the hardware and software which allows for the promised advanced capabilities. The aim of this thesis was to present results from an experiment undertaken using the Hermanus DPS-4D (34.4°S 19.2°E, South Africa), the first of this version to be installed globally, to answer a science question outside of the normally expected capabilities of an ionosonde. The science question posed focused on the ability of the DPS-4D to provide information on day-time Pc3 pulsations evident in the ionosphere. Day-time Pc3 ULF waves propagating down through the ionosphere cause oscillations in the Doppler shift of High Frequency (HF) radio transmissions that are correlated with the magnetic pulsations recorded on the ground. Evidence is presented which shows that no correlation exists between the ground magnetic pulsation data and DPS-4D ionospheric data. The conclusion was reached that although the DPS-4D is more advanced in its eld of technology than its predecessors it may not be used to observe Pc3 pulsations.

Mars is the fourth planet from the Sun and its interaction with the solar wind is a quite interesting subject tostudy. While it is a rocky planet it doesn't have an intrinsic magnetic eld, but an ionosphere, created by thephotoionization of a relatively thin atmosphere. In addition there are magnetic "patches" on its surface, remnantsof an ancient fossilized magnetic eld. All these factors make the study of its interaction with the solar wind quiteintriguing. In this work we tried to extract information about the electron population and the magnetic eld intensity aroundthe planet, but also about the corresponding pressures to those magnitudes: electron -thermal- and magneticpressure respectively. Also, we tried to determine the position of the magnetic pileup boundary (MPB) andcompare it to the theoretical one, and lastly, we search for any possible structures along the MPB -both aboveand below it- by analyzing the ratio of the above mentioned pressures.We used data collected by Mars AdvancedRadar for Subsurface andIonosphereSounding (MARSIS), in a period of almost 9 years - December 2005 to May2014.

published_or_final_version / Physics / Master / Master of Science

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.