The solar wind has an important impact on the Earth and its magnetic field. Among the solar wind perturbations, there can be jumps in the solar wind dynamic pressure as well as strong magnetic excursions in the z-component of the Interplanetary Magnetic Field (IMF B_(Z )). When coronal mass ejections and other solar disturbances take place in the solar wind, there can be clear changes in the global geomagnetic field, as measured by a magnetic index called Sym-H. In this thesis some unusual events were found for which there were large fluctuations either in the solar wind dynamic pressure or in the IMF B_Z but not simultaneously in both. These events suggest that the response of the geomagnetic field to the dynamic pressure fluctuations of the solar wind is variable. In particular, it was found that the earthward component (x-component) of the IMF appeared to influence the magnitude of the Sym-H response. By contrast, there was no visible impact of the y-component of the IMF. In a second exceptional event it was found that the IMF was changing substantially while the solar wind dynamic pressure remained very constant. From this study a time delay between the IMF B_Z component and the resulting Sym-H was found to be of the order of 60 to 90 minutes.

A three-dimensional (3D) steady-state electron modulation model based on Parker (1965) transport equation is applied to study the modelling of – 7 MeV galactic and Jovian electrons in the inner heliosphere. The latter is produced within Jupiter's magnetosphere which is situated at - 5 AU in the ecliptic plane. The heliospheric propagation of these particles is mainly described by the heliospheric diffusion tensor. Some elements of the tensor, such as the diffusion coefficient in the azimuthal direction, which were neglected in the previous two-dimensional modulation studies are investigated to account for the three-dimensional transport of Jovian electrons. Different anisotropic solar wind speed profiles that could represent solar minimum conditions were modelled and their effects were illustrated by computing the distribution of 7 MeV Jovian electrons in the equatorial regions. In particular, the electron intensity time-profile along the Ulysses spacecraft trajectory was calculated for these speed profiles and compared to the 3-10 MeV electron flux observed by the Kiel Electron Telescope (KET) on board the Ulysses spacecraft from launch (1990) up to end of its first out-of-ecliptic orbit (2000). It was found that the model solution computed with the solar wind profile previously assumed for typical solar minimum conditions produced good compatibility with observations up to 1998. After 1998 all model solutions deviated completely from the observations. In this study, as a further attempt to model KET observations more realistically, a new relation is established between the latitudinal dependence of the solar wind speed and the perpendicular polar diffusion. Based on this relation, a transition of an average solar wind speed from solar minimum conditions to intermediate solar activity and to solar maximum conditions was modelled based on the assumption of the time-evolution of large polar coronal holes and were correlated to different scenarios of the enhancement of perpendicular polar diffusion. Effects of these scenarios were illustrated, as a series of steady-state solutions, on the computed 7 MeV Jovian and galactic electrons in comparison with the 3-10 MeV electron observed by the KET instrument from the period 1998 up to the end of 2003. Subsequent effects of these scenarios were also shown on electron modulation in general. It was found that this approach improved modelling of the post-1998 discrepancy between the model and KET observations but it also suggested the need for a time-dependent 3D electron modulation model to describe modulation during moderate to extreme solar maximum conditions. / Thesis (M.Sc.)--North-West University, Potchefstroom Campus, 2004.

A two dimensional hydrodynamic model describing the solar wind interaction with the local interstellar medium, which surrounds the solar system, is used to study the heliosphere both as a steady-state- and dynamic structure. The finite volume method used to solve the associated system of hydrodynamic equations numerically is discussed in detail. Subsequently the steady state heliosphere is studied for both the case where the solar wind and the interstellar medium are assumed to consist of protons only, as well as the case where the neutral hydrogen population in the interstellar medium is taken into account. It is shown that the heliosphere forms as three waves, propagating away from the initial point of contact between the solar wind and interstellar matter, become stationary. Two of these waves become stationary at sonic points, forming the termination shock and bow shock respectively. The third wave becomes stationary as a contact discontinuity, called the heliopause. It is shown that the position and geometry of the termination shock, heliopause and bow shock as well as the plasma flow characteristics of the heliosphere largely depend on the dynamic pressure of either the solar wind or interstellar matter. The heliosphere is modelled as a dynamic structure, including both the effects of the solar cycle and short term variations in the solar wind observed by a range of spacecraft over the past ~ 30 years. The dynamic model allows the calculation of an accurate record of the heliosphere state over the past ~ 30 years. This record is used to predict the time at which the Voyager 2 spacecraft will cross the termination shock. Voyager 1 observations of 10 MeV cosmic ray electrons are then used in conjunction with a cosmic ray modulation model to constrain the record of the heliosphere further. It is shown that the dynamic hydrodynamic model describes the heliosphere accurately within a margin of error of ±0.7 years and ±3 AU. The model predicts that Voyager 2 crossed the termination shock in 2007, corresponding to preliminary results from observations indicating that the crossing occurred in August 2007. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.

A three-dimensional (3D) steady-state electron modulation model based on Parker (1965) transport equation is applied to study the modelling of – 7 MeV galactic and Jovian electrons in the inner heliosphere. The latter is produced within Jupiter's magnetosphere which is situated at - 5 AU in the ecliptic plane. The heliospheric propagation of these particles is mainly described by the heliospheric diffusion tensor. Some elements of the tensor, such as the diffusion coefficient in the azimuthal direction, which were neglected in the previous two-dimensional modulation studies are investigated to account for the three-dimensional transport of Jovian electrons. Different anisotropic solar wind speed profiles that could represent solar minimum conditions were modelled and their effects were illustrated by computing the distribution of 7 MeV Jovian electrons in the equatorial regions. In particular, the electron intensity time-profile along the Ulysses spacecraft trajectory was calculated for these speed profiles and compared to the 3-10 MeV electron flux observed by the Kiel Electron Telescope (KET) on board the Ulysses spacecraft from launch (1990) up to end of its first out-of-ecliptic orbit (2000). It was found that the model solution computed with the solar wind profile previously assumed for typical solar minimum conditions produced good compatibility with observations up to 1998. After 1998 all model solutions deviated completely from the observations. In this study, as a further attempt to model KET observations more realistically, a new relation is established between the latitudinal dependence of the solar wind speed and the perpendicular polar diffusion. Based on this relation, a transition of an average solar wind speed from solar minimum conditions to intermediate solar activity and to solar maximum conditions was modelled based on the assumption of the time-evolution of large polar coronal holes and were correlated to different scenarios of the enhancement of perpendicular polar diffusion. Effects of these scenarios were illustrated, as a series of steady-state solutions, on the computed 7 MeV Jovian and galactic electrons in comparison with the 3-10 MeV electron observed by the KET instrument from the period 1998 up to the end of 2003. Subsequent effects of these scenarios were also shown on electron modulation in general. It was found that this approach improved modelling of the post-1998 discrepancy between the model and KET observations but it also suggested the need for a time-dependent 3D electron modulation model to describe modulation during moderate to extreme solar maximum conditions. / Thesis (M.Sc.)--North-West University, Potchefstroom Campus, 2004.

A two dimensional hydrodynamic model describing the solar wind interaction with the local interstellar medium, which surrounds the solar system, is used to study the heliosphere both as a steady-state- and dynamic structure. The finite volume method used to solve the associated system of hydrodynamic equations numerically is discussed in detail. Subsequently the steady state heliosphere is studied for both the case where the solar wind and the interstellar medium are assumed to consist of protons only, as well as the case where the neutral hydrogen population in the interstellar medium is taken into account. It is shown that the heliosphere forms as three waves, propagating away from the initial point of contact between the solar wind and interstellar matter, become stationary. Two of these waves become stationary at sonic points, forming the termination shock and bow shock respectively. The third wave becomes stationary as a contact discontinuity, called the heliopause. It is shown that the position and geometry of the termination shock, heliopause and bow shock as well as the plasma flow characteristics of the heliosphere largely depend on the dynamic pressure of either the solar wind or interstellar matter. The heliosphere is modelled as a dynamic structure, including both the effects of the solar cycle and short term variations in the solar wind observed by a range of spacecraft over the past ~ 30 years. The dynamic model allows the calculation of an accurate record of the heliosphere state over the past ~ 30 years. This record is used to predict the time at which the Voyager 2 spacecraft will cross the termination shock. Voyager 1 observations of 10 MeV cosmic ray electrons are then used in conjunction with a cosmic ray modulation model to constrain the record of the heliosphere further. It is shown that the dynamic hydrodynamic model describes the heliosphere accurately within a margin of error of ±0.7 years and ±3 AU. The model predicts that Voyager 2 crossed the termination shock in 2007, corresponding to preliminary results from observations indicating that the crossing occurred in August 2007. / Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.

Dans cette thèse nous avons présenté un modèle probabiliste auto cohérent décrivant la relaxation d'un faisceau d'électrons dans un vent solaire dont les fluctuations aléatoires de la densité ont les mêmes propriétés spectrales que celles mesurées à bord de satellites. On a supposé que, le système possédait différentes échelles caractéristiques en plus de l'échelle caractéristique des fluctuations de densité. Ceci nous a permis de décrire avec précision l'interaction onde-particule à des échelles inférieures à l'échelle caractéristique des fluctuations de densité en supposant que des paramètres d'onde sont connus: notamment, la phase, la fréquence et l'amplitude. Cependant, pour des échelles suffisamment plus grandes que l'échelle caractéristique des irrégularités de densité, l'interaction des ondes et des particules ne peut être caractérisée déterminé que par des quantités statistiques moyennes dans l'espace des vitesses à savoir: le taux de croissance/amortissement et le coefficient de diffusion des particules. En utilisant notre modèle, nous décrivons l'évolution de la fonction de distribution des électrons et d'énergie des ondes de Langmuir. Le schéma 1D suggérée est applicable pour des paramètres physiques de plasma du vent solaire à différentes distances du Soleil. Ainsi, nous pouvons utiliser nos calculs pour décrire des émissions solaires de Type III, ainsi que les interactions de faisceau avec le plasma, à des distances d'une Unité Astronomique du Soleil dans l'héliosphère et au voisinage des chocs planétaires. / This thesis is dedicated to effects of plasma density fluctuations in the solar wind on the relaxation of the electron beams ejected from the Sun. The density fluctuations are supposed to be responsible for the changes in the local phase velocity of the Langmuir waves generated by the beam instability. Changes in the wave phase velocity during the wave propagation can be described in terms of probability distribution function determined by distribution of the density fluctuations. Using these probability distributions we describe resonant wave particle interactions by a system of equations, similar to well known quasi-linear approximation, where the conventional velocity diffusion coefficient and the wave growth rate are replaced by the averaged in the velocity space. It was shown that the process of relaxation of electron beam is accompanied by transformation of significant part of the beam kinetic energy to energy of the accelerated particles via generation and absorption of the Langmuir waves. We discovered that for the very rapid beams the relaxation process consists of two well separated steps. On first step the major relaxation process occurs and the wave growth rate almost everywhere in the velocity space becomes close to zero or negative. At the seconde stage the system remains in the state close to state of marginal stability enough long to explain how the beam may be preserved traveling distances over 1 AU while still being able to generate the Langmuir waves.

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Made available in DSpace on 2014-12-17T14:57:37Z (GMT). No. of bitstreams: 1 BrismarkGR_capa_ate_secao3.pdf: 558121 bytes, checksum: b18dbb5797c3daa771ffa68209743702 (MD5) Previous issue date: 2007-07-30 / This work purposes the application of a methodology to optimize the implantation cost of an wind-solar hybrid system for oil pumping. The developed model is estimated the implantation cost of system through Multiple Linear Regression technique, on the basis of the previous knowledge of variables: necessary capacity of storage, total daily energy demand, wind power, module power and module number. These variables are gotten by means of sizing. The considered model not only can be applied to the oil pumping, but also for any other purposes of electric energy generation for conversion of solar, wind or solar-wind energy, that demand short powers. Parametric statistical T-student tests had been used to detect the significant difference in the average of total cost to being considered the diameter of the wind, F by Snedecor in the variance analysis to test if the coefficients of the considered model are significantly different of zero and test not-parametric statistical by Friedman, toverify if there is difference in the system cost, by being considered the photovoltaic module powers. In decision of hypothesis tests was considered a 5%-significant level. The configurations module powers showed significant differences in total cost of investment by considering an electrical motor of 3 HP. The configurations module powers showed significant differences in total cost of investment by considering an electrical motor of 5 HP only to wind speed of 4m/s and 6 m/s in wind of 3 m, 4m and 5 m of diameter. There was not significant difference in costs to diameters of winds of 3 m and 4m. The mathematical model and the computational program may be used to others applications which require electrical between 2.250 W and 3.750 W. A computational program was developed to assist the study of several configurations that optimizes the implantation cost of an wind-solar system through considered mathematical model / Este trabalho prop?e a aplica??o de uma metodologia para otimizar o custo da implanta??o de um sistema h?brido e?lico-solar para bombeamento de petr?leo. O modelo desenvolvido estima o custo da implanta??o do sistema por meio da utiliza??o da t?cnica de Regress?o Linear M?ltipla, com base no conhecimento pr?vio das vari?veis: capacidade necess?ria de armazenamento, demanda di?ria total de energia, pot?ncia do aerogerador, pot?ncia de m?dulos e n?mero de m?dulos, sendo estas vari?veis obtidas por meio de dimensionamento. O modelo proposto pode ser aplicado n?o somente ao bombeamento de petr?leo, mas tamb?m para quaisquer outras finalidades de gera??o de energia el?trica por convers?o da energia e?lica, solar ou e?lica-solar que demandem baixas pot?ncias. Foram utilizados testes estat?sticos param?tricos tais como o T-student, para detectar a diferen?a significativa na m?dia do custo total ao ser considerado o di?metro do aerogerador; o F de Snedecor, na an?lise de vari?ncia para testar se os coeficientes do modelo proposto s?o significativamente diferentes de zero e o teste estat?stico n?o-param?trico de Friedman, para verificar se existe diferen?a no custo do sistema, ao ser considerado as pot?ncias dos m?dulos fotovoltaicos. Na decis?o dos testes de hip?teses considerou-se um n?vel de signific?ncia de 5%. As configura??es de pot?ncias dos m?dulos apresentaram diferen?as significativas no custo total do investimento ao ser considerado um motor el?trico de 3 HP. As configura??es de pot?ncias dos m?dulos apresentaram diferen?as significativas com motor el?trico de 5 HP somente para velocidades de vento de 4 m/s e 6 m/s em aerogeradores de 3 m, 4 m e 5 m de di?metros. N?o existiu diferen?a significativa nos custos para di?metros de aerogeradores de 3 m e 4 m. O modelo matem?tico e o programa computacional podem ser utilizados para outras aplica??es que requeiram pot?ncia el?trica entre 2.250 W e 3.750 W. Desenvolveu-se um programa computacional para auxiliar o estudo de v?rias configura??es, o qual otimiza o custo de implanta??o de um sistema e?lico-solar com base no modelo matem?tico proposto

Depuis la découverte de la faculté d'un instrument radio à détecter les poussières, plusieurs études ont été menées afin de mieux exploiter ce type d'instrument. Le présent travail concerne l'exploitation et l'interprétation des observations de poussières de l'instrument WAVES à bord des deux sondes STEREO à 1 UA, ainsi que la modélisation de leur dynamique dans le milieu interplanétaire. Cette thèse a débuté avec une étude des mesures de poussières de taille micro-métrique. Les résultats ont montré que les données étaient pertinentes dans le sens où malgré les incertitudes sur les données et les simplifications de la modélisation du flux, les mesures de direction fournies par cet instrument sont au moins aussi précises que celles fournies par les instruments conventionnels. Ensuite, nous avons réalisé une étude sur les observations de nanoparticules à 1 UA. Nous avons montré qu'une impulsion caractéristique d'un impact d'une nanoparticule se forme suite à la perturbation temporaire du courant de retour de photo-électrons de l'antenne électrique la plus proche du point d'impact. La comparaison des flux mesurés et déduits des observations réalisées dans deux domaines différents (temporel et fréquentiel) montre une cohérence entre les mesures. Enfin, la modélisation de la dynamique des nanoparticules appuie le fait que des nanoparticules crées près du Soleil sont accélérées par le vent solaire et peuvent atteindre 300 km/s à 1 UA. L'analyse statistique des résultats de cette étude à 1 UA a montré une cohérence avec les mesures obtenues sur STEREO, mais aussi avec l'interprétation de ces mesures et l'estimation de la charge du nuage de plasma. / Since the discovery of the ability of a radio instrument to detect dust, several studies have been conducted to determine the physical phenomena underlying measures, the fluxes, and the dust characteristics which can be determined. The present work concerns the exploitation and the interpretation of dust observations made by WAVES instrument onboard the two STEREO probes at 1 AU, as well as modeling of dust dynamics in the interplanetary medium. This thesis began with a study of the sub-micron dust data. The results of this study showed that these data were relevant in the sense that despite the uncertainties on the data and the simplified modeling of the flux, the measurements of the direction provided by this instrument are at least as accurate as those provided by conventional instruments. We, thereafter, began a study of observations of nanoparticles at 1 AU. We showed that a typical pulse generated by a nanoparticle impact is formed by the temporary disruption of the photo-electrons return current of the antenna which is closest to the point of impact. In addition, the comparison of measured and inferred flux observations in two different domains (time and frequency) shows a consistency and agreement between measurements. Finally, the modeling of the dynamics of nanoparticles supports the fact that nanoparticles created near the Sun are accelerated by the solar wind and can reach 300 km/s at 1 AU. Statistical analysis of the results of this study to 1 AU showed a consistency with the measurements obtained with STEREO data, and also with the interpretation of these measurements and the estimation of the electric charge of the plasma cloud

La turbulence dans le vent solaire a suscité beaucoup d'intérêt depuis les premières mesures in-situ dans l'héliosphère. Mais de nombreuses questions sont encore sans réponse. En particulier, le rôle de la turbulence dans le chauffage du vent solaire ainsi que la nature de la turbulence autour des échelles ioniques, là où les fluctuations turbulentes sont supposées être dissipées. À travers une étude multi-satellite incluant les sondes Helios 2, Stereo et Ulysses, nous avons montré qu'à grande échelle, dans le domaine inertiel, il existe une forte corrélation entre la pression thermique des ions et l'amplitude des fluctuations magnétiques. Cette corrélation est observée de 0,3 à 5,4 unités astronomiques. Elle pourrait s'expliquer soit par la présence d'une corrélation fossile déjà présente dans la photosphère ou la couronne solaire ; soit par le fait que le vent solaire est chauffé par la turbulence. Par la suite, nous nous sommes concentrés sur les échelles ioniques, où le spectre turbulent forme un coude. Grâce à la transformée en ondelettes, nous avons mis en évidence la présence d'ondes d'Alfvén de faibles amplitudes, ainsi que celle de couches de courant et vortex d'Alfvén de fortes amplitudes. Nous avons aussi mis en place un nouveau formalisme basé sur une fonction de quatre paramètres permettant de décrire la statistique des fluctuations magnétiques dans le vent solaire. Cette description s'applique des échelles MHD aux échelles électroniques. En utilisant deux approches différentes, l'analyse locale et l'analyse statistique des fluctuations, nous avons établi un lien entre l'évolution de l'intermittence et celle du spectre turbulent aux échelles ioniques. / Turbulence in the solar wind has been attracting attention since first in-situ measurements in the Heliosphere. Still a lot of open questions remain. In particular, the role of turbulence in the solar wind heating as well as its nature around plasma kinetic scales, where turbulent fluctuations are supposed to be dissipated. Through a multi-satellite analysis including Helios 2, Stereo and Ulysses probes, we were able to show that at large-scale, in the inertial range, there exist a strong correlation between the ion thermal pressure and the amplitude of magnetic fluctuations, which maintains between 0.3 and 5.4 astronomical units. The origine of this correlation can be (i) a fossil correlation present already in the photosphere or in the solar corona; or (ii) the solar wind heating by the turbulence. This heating is expected to take place at plasma kinetic scales.Subsequently we focused on ionic scales, where the turbulent spectrum has a break. Thanks to wavelet transform and phase coherence analysis we shed light on the nature of turbulence around the spectral break: we show the presence of small amplitude Alfvén waves as well as strong amplitude current sheets and Alfvén vortices. We proposed as well new statistical description of magnetic fluctuations in the solar wind by using a four-parameter function, valid from MHD to electron scales. Using two different approaches, detail analysis of fluctuations and statistical analysis, we established the connection between intermittency and the evolution of the turbulent spectrum at ion scales.