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.

Spread F is a phenomenon of the ionosphere in which the pulses returned from the ionosphere are of a much greater duration than the transmitted ones. The occurrence of spread F can be predicted using the technique of Neural Networks (NNs). This thesis presents the development and evaluation of NN based models (two single station models and a regional model) for predicting the occurrence of spread F over selected stations within the Brazilian sector. The input space for the NNs included the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), magnetic index (measure of the magnetic activity) and magnetic position (latitude, magnetic declination and inclination). Twelve years of spread F data measured during 1978 to 1989 inclusively at the equatorial site Fortaleza and low latitude site Cachoeira Paulista are used in the development of an input space and NN architecture for the NN models. Spread F data that is believed to be related to plasma bubble developments (range spread F) were used in the development of the models while those associated with narrow spectrum irregularities that occur near the F layer (frequency spread F) were excluded. The results of the models show the dependency of the probability of spread F as a function of local time, season and latitude. The models also illustrate some characteristics of spread F such as the onset and peak occurrence of spread F as a function of distance from the equator. Results from these models are presented in this thesis and compared to measured data and to modelled data obtained with an empirical model developed for the same purpose.

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.

From Introduction: The minimum in the scalar magnitude of the geographic total field, which lies off the coast of Brazil, allows the mirror points of trapped particles to dip low into the atmosphere over the South Atlantic Ocean, resulting in two regions of maximum intensity of preciptated particles in that region, one from the inner belt and one from the outer. High charged particle fluxes have been observed at low altitudes over these regions by satellites Sputnik 5 and 6 (Ginsburg et al, 1961) and Discoverer 31 (Seward and Kornblum, 1963) amongst others. The more southerly of these two regions acts as a sink for electrons from the outer radiation belt and will be referred to in what follows as the Southern Radiation Anomaly. Gladhill and van Rooyen (1963) predicted that the energy deposited in the upper atmosphere by these charged particles would be sufficient to give rise to enhanced geophysical effects such as auroral emission, X-rays and ionization and heating of the upper atmosphere in this region. Although some of these effects have been correlated with precipitated electrons, no definite relation had until now been established between ionospheric effects and precipitated particles. The aim of this thesis was to investigate such a relationship and the results were extremely successful. It will be shown conclusively in what follows, that the precipitation of electrons can account for the ionospheric disturbances defined by a disturbance criterion at all stations around L=4. Part I describes the exploration of the radiation belts and the magnetosphere with rockets and satellites. The resulting theoretical models based on the observations are discussed. A brief review is given of the work that has been done to date to derive equations for the loss and replenishment of particles in the belts. Because of the complexity of these and the number of doubtful factors involved, a simple model of injection of electrons into the outer belt is devised, giving average values of trapped and precipitated electron fluxes at any point around L=4. In Part II, this model is employed together with the disturbance criterion of Gledhill and Torr (1965) to examine the relationship between ionospheric disturbances and electron fluxes. Also the energy range of the precipitated particles is examined.

As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.

Abstract From the very beginning of modern ionospheric science, different radar applications have been utilised in ionospheric measurements. The most sophisticated ionospheric radars are the incoherent scatter radars, which detect the extremely weak scattering of radio waves from thermal fluctuations in the ionospheric plasma. Besides the low signal level, the stochastic nature of the scattering process causes further complications to the measurements. The scattering produces a zero-mean random signal, whose autocorrelation function contains the information of the ionospheric plasma parameters. Incoherent scatter radars have been used for about half a century, but the demanding task of developing transmission modulation and data analysis is still in progress. In this thesis, a statistical inversion based method for removing range ambiguities from the autocorrelation functions, lag profile inversion, is applied to incoherent scatter radar data. The data have been recorded with the EISCAT incoherent scatter radars, located in Northern Fennoscandia. The method is first applied to standard EISCAT experiments, the results giving strong evidence that the method is applicable for the purpose, and it provides results of at least equal quality with the present standard methods. In subsequent studies, new radar modulation methods are developed, which may provide significant improvements to the present incoherent scatter radar experiments. All the methods have been tested with a real radar, and lag profile inversion has been successfully applied to the recorded data. The methods are also put to use in order to measure the predicted effects of artificial heating of the free electrons in the D-region of the ionosphere.

No description available.

The Sub-Auroral Polarization Stream (SAPS) is a narrow, intense and persistent westward (sunward) ionospheric convection flow channel observed equatorward of the auroral electron precipitation boundary, predominantly on the nightside. Previous studies have identified disturbed-time SAPS to be a geomagnetic activity dependent phenomenon, which exhibits average pre-midnight and post-midnight velocities of 1000 m/s and 400 m/s respectively. Numerous studies have reported even narrower and more intense westward plasma flows called SAIDs to be embedded within SAPS channels, especially during substorm recovery phases. Quiet-time SAPS studies, although relatively few, have shown these SAPS to be associated with much weaker velocities and to be influenced by substorm intensifications. However, these studies have been limited in their ability to make simultaneous measurements of SAPS flow velocities over many hours of MLT. The recent expansion of SuperDARN radars to middle latitudes facilitates unprecedented large-scale observations of SAPS over 10 hours of MLT with high temporal and spatial resolution. In this thesis, we first examine the spatial and temporal dynamics of one quiet-time SAPS event, using the mid-latitude SuperDARN radars. The SAPS was identified as elevated flows lying equatorward of the auroral electron precipitation boundary specified by the NOAA POES satellites. We demonstrate the L-shell fitting technique to analyze the dynamics in the strength and direction of the two-dimensional SAPS flow velocities at three separate magnetic longitudes. The quiet-time SAPS event thus examined lasted for over 4 hours in UT and extended over 10 hours of MLT, as is commonly observed for disturbed-time SAPS. However, the decrease in SAPS peak latitudes and peak velocities with MLT and MLon respectively, observed for disturbed-time SAPS, was not observed for this event. We also find the dynamics of the enhancements in the quiet-time SAPS peak velocities, to correlate well with that of substorm intensifications identified using the CARISMA magnetometers. We then identify numerous such conjunctions between quiet-time SAPS and substorms to infer that quiettime SAPS were almost always associated with substorms and their durations were well bounded by that of the substorms for most cases. Next, we extend this analysis over to a statistical study of quiet-time and disturbed-time SAPS events identified over two years. From this study, we find quiet-time SAPS to occur between the relatively narrow nightside MLT range of [18, 4] whereas disturbed-time SAPS was found to occur between the broader nightside MLT range of [15, 5]. We also find the occurrence percentage of quiet-time SAPS to be at its highest between the narrow latitude range of 60-66⁰, while disturbed-time SAPS was observed to occur within a much broader latitude range of 55-66⁰. Finally, the calibration and validation of a control card used in the SuperDARN radar transmitters, is discussed. / Master of Science

The Scintillation Prediction Observation Research Task (SPORT) is a joint United States of America (USA) and Brazil small satellite mission to address the further under-standing of the preconditions leading to equatorial plasma bubbles. Utah State University (USU) is supplying four instruments towards this SPORT mission. These four instruments will allow measurements of the electric field and plasma density in the ionosphere which will help understand what gives rise to plasma bubbles in the ionosphere. This thesis will discuss the command, control, and telemetry communications needed to operate the SPORT USU instruments. It will cover an overview of the instruments involved, how the instruments are controlled specifically, what commands were needed to run the instruments, what telemetry data was produced and how it was transmitted to the ground station, and how the data is made useful. The design process, challenges, and solutions to this system and project will also be discussed.

The ionospheres of Venus and Mars are important components of the planet-space boundary that play a major role in atmospheric escape processes. Characterization of these regions reveals the physical processes that control them and provides a foundation for more detailed studies of chemistry, dynamics, and energetics. At both planets the ionospheres contain two layers: the main layer, which is formed by photoionization from extreme ultraviolet radiation (EUV, λ<120 nm), and the lower layer, which is formed by photoionization from soft X-rays (SXRs, λ<10 nm) and subsequent electron impact ionization. In this dissertation I investigate how the solar EUV and SXR irradiance controls these layers at Venus and Mars. First, I develop an empirical model of the ultraviolet (UV, λ<190 nm) solar spectrum as a function of F10.7, which is a commonly used proxy of the UV irradiance. I derive power-law relationships between F10.7 and the ionizing irradiance for five neutral species and show that the relationships are nonlinear. These relationships can be used to estimate the EUV irradiance when no solar spectrum measurements are available. Second, I show that the peak electron densities in the ionospheres of Venus and Mars are proportional to the square-root of the ionizing irradiance, which is in contrast to previous studies that have used F10.7 as their representation of the UV irradiance. This finding ameliorates a discrepancy between theory and observations and is in agreement with the prediction that dissociative recombination is the main ion loss mechanism near the ionospheric peaks at Venus and Mars. Third, using a numerical model and electron density profiles from Venus Express, I examine the behavior of the peak altitude, peak density, and morphology of the lower layer at Venus. I show that the peak altitudes and densities in the lower and main layers vary similarly with solar zenith angle (SZA). This implies that neutral and electron thermal gradients at these altitudes vary little with SZA. I also show that, compared to the main layer, the lower layer morphology and peak density varies more over the solar cycle due to the hardening of the solar spectrum.