Cette expérience en fusée, qui s'inscrit dans le cadre des études d'interaction onde-particule dans la magnétosphère, a montré l'absence de relation entre les particules et les ondes TBF de type souffle et choeur de l'aube détectées simultanément à bord. On a cherché, par une méthode de trace de rayons, la source des émissions qui se situent dans la plasmapause.

This thesis discusses the reasons for space exploration and space science. Space plasma physics is identified as an essential building block to understand the space environment and it is argued that observation and analysis of space plasma waves is an important approach. Space plasma waves are the main actors in many important processes. So-called broadband waves are found responsible for much of the ion heating in the auroral region. We investigate the wave properties of broadband waves and show that they can be described as a mixture of electrostatic wave modes. In small regions void of cold electrons the broadband activity is found to be ion acoustic waves and these regions are also identified as acceleration regions. The identification of the wave modes includes reconstructions of the wave distribution function. The reconstruction technique allow us to determine the wave vector spectrum, which cannot be measured directly. The method is applied to other wave events and it is compared in some detail with a similar method. Space plasma wave are also sensitive tools for investigations of both the fine-structure and the dynamics of space plasmas. Studies of whistler mode waves observed in the boundary layer on the magnetospheric side of the magnetopause reveal that the plasma is organized in tube-like structures moving with the plasma drift velocity. The perpendicular dimension of these tubes is of the order of the electron inertial length. We present evidence that each tube is linked to a reconnection site and argue that the high density of tube-like structures indicates patchy reconnection.

The contemporary terrestrial atmosphere loses matter at a rate of around 100,000 tons per year. A major fraction of the net mass loss is constituted by ions, mainly H+ and O+, which escape from the Earth’s ionosphere in the polar regions. Previously, the outflow has only been measured at low altitudes, but to understand what fraction actually escapes and does not return, the measurements should be conducted far from the Earth. However, at large geocentric distances the outflowing ions are difficult to detect with conventional ion instruments on spacecraft, since the spacecraft electrostatic potential normally exceeds the equivalent energy of the ions. This also means that little is known about the ion outflow properties and distribution in space far from the Earth. In this thesis, we present a new method to measure the outflowing low-energy ions in those regions where they previously have been invisible. The method is based on the detection by electric field instruments of the large wake created behind a spacecraft in a flowing, low-energy plasma. Since ions with low energy will create a larger wake, the method is more sensitive to light ions, and our measured outflow is essentially the proton outflow. Applying this new method on data from the Cluster spacecraft, we have been able to make an extensive statistical study of ion outflows from 5 to 19 Earth radii in the magnetotail lobes. We show that cold proton outflows dominate in these large regions of the magnetosphere in both flux and density. Our outflow values of low-energy protons are close to those measured at low altitudes, which confirms that the ionospheric outflows continue far back in the tail and contribute significantly to the magnetospheric content. We also conclude that most of the ions are escaping and not returning, which improves previous estimates of the global outflow. The total loss of protons due to high-latitude escape is found to be on the order of 1026 protons/s.

WINDMI is a low dimensional plasma physics-based model of the coupled magnetosphere-ionosphere system. The nonlinear system of ordinary differential equations describes the energy balance between the basic nightside components of the system using the solar wind driving voltage as input. Of the eight dynamical variables determined by the model, the region 1 field aligned current and ring current energy is compared to the westward auroral electrojet AL index and equatorial geomagnetic disturbance storm time Dst index. The WINDMI model is used to analyze the magnetosphere-ionosphere system during major geomagnetic storms and substorms which are community campaign events. Numerical experiments using the WINDMI model are also used to assess the question of how much interplanetary shock events contribute to the geoeffectiveness of solar wind drivers. For two major geomagnetic storm intervals, it is found that the magnetic field compressional jump is important to producing the changes in the AL index. Further, the WINDMI model is implemented to compute model AL and Dst predictions every ten minutes using real-time solar wind data from the ACE satellite as input. Real-Time WINDMI has been capturing substorm and storm activity, as characterized by the AL and Dst indices, reliably since February 2006 and is validated by comparison with ground-based measurements of the indices. Model results are compared for three different candidate input solar wind driving voltage formulas. Modeling of the Dst index is further developed to include the additional physical processes of tail current increases and sudden commencement. A new model, based on WINDMI, is developed using the dayside magnetopause and magnetosphere current systems to model the magnetopause boundary motion and the dayside region 1 field aligned current which is comparable to the auroral upper AU index. / text

The Auroral Acceleration Region (AAR) is a key region in understanding the interactionbetween the Magnetosphere and Ionosphere. To understand the physical, spatial, and temporal features of the region, multi-point measurements are required. Distributed small-satellite missions such as constellations of multiple nano satellites (for example multi-unit CubeSats) would enable such type of measurements. The capabilities of such a mission will highly depend on the number of satellites - one reason that makes low-cost platforms like CubeSats a very promising choice. In a previous study, the state-of-the-art of miniaturized payloads for AAR measurements was analyzed and evaluated on the capabilities of different multi-CubeSat configurations equipped with such payloads in addressing different open questions in AAR. This thesis will provide the mission analysis of such a multi-CubeSat mission to the AAR and possible mission design. This includes defining the mission scenario and associated requirements, developing a mathematical description of AAR that allows for specific regions in space to be targeted, an optimisation process for designing orbits targeting these regions, conversion of a satellite formation to appropriate orbits, verifying the scientific performance of this formation and the various costs associated with entering, maintaining, and exiting these orbits.

A in uência do caráter inomogêneo da região-fonte na ampli cação da Radiação Quilom étrica das Auroras é investigada. Inicialmente é feita uma revisão de trabalhos relevantes publicados a respeito do mesmo tema geral, tanto os que concernem aos dados observacionais como os que concernem aos modelos teóricos e simulações numéricas. Esta revisão é precedida pelo estabelecimento de conceitos e de nições pertinentes ao tema. São consideradas duas abordagens distintas na determinação da ampli cação da radiação na região-fonte. A primeira considera o plasma localmente homogêneo, enquanto a segunda toma em conta, explicitamente, a contribuição dos gradientes dos parâmetros do plasma. A ampli cação da radiação é determinada pela avaliação do tensor dielétrico do plasma e pela evolução da radia ção através do estudo de traçado de raios. Os parâmetros do plasma são obtidos através de uma formulação autoconsistente que toma em conta uma queda de potencial elétrico ao longo das linhas de campo geomagnético. Utiliza-se um modelo de lâmina auroral em que o campo magnético ambiente é considerado localmente homogêneo. O modelo teórico subjacente adotado é o do maser de elétron-cíclotron. O principal resultado obtido revela uma diminuição na ampli cação nal por um fator em torno de três, quando os gradientes dos parâmetros do plasma são considerados explicitamente. Este resultado pode ter implicações na capacidade do maser de elétron-cíclotron em explicar os níveis de radiação mais elevados observados. / The in uence from source region inhomogeneous character on ampli cation of Auroral Kilometric Radiation is investigated. Firstly, a review over relevant works published about the same general theme is made, concerning about observational data as well theoretical models and numerical simulations. This review is preceded by the establishment of de nitions and concepts related to the theme. Two distinct approaches are considered in determining the ampli cation of radiation across the source region. First approach takes the plasma as locally homogeneous, while second approach account, explicitly, for gradients on plasma parameters. The ampli cation is obtained through evaluation of the dielectric tensor and the evolution of radiation through ray tracing. Plasma parameters are obtained using a self-consistent formulation which account for an electric potential drop along geomagnetic eld lines. An auroral slab model is used where the ambient magnetic eld is taken as locally homogeneous. The subjacent theoretical model adopted is the electron-cyclotron maser. The main result obtained reveals a reduction on nal ampli cation by a factor about three, when plasma parameters gradients are explicitly accounted. This nding may have implications on capability of electron-cyclotron maser for explanation the most intense levels of radiation observed.

A in uência do caráter inomogêneo da região-fonte na ampli cação da Radiação Quilom étrica das Auroras é investigada. Inicialmente é feita uma revisão de trabalhos relevantes publicados a respeito do mesmo tema geral, tanto os que concernem aos dados observacionais como os que concernem aos modelos teóricos e simulações numéricas. Esta revisão é precedida pelo estabelecimento de conceitos e de nições pertinentes ao tema. São consideradas duas abordagens distintas na determinação da ampli cação da radiação na região-fonte. A primeira considera o plasma localmente homogêneo, enquanto a segunda toma em conta, explicitamente, a contribuição dos gradientes dos parâmetros do plasma. A ampli cação da radiação é determinada pela avaliação do tensor dielétrico do plasma e pela evolução da radia ção através do estudo de traçado de raios. Os parâmetros do plasma são obtidos através de uma formulação autoconsistente que toma em conta uma queda de potencial elétrico ao longo das linhas de campo geomagnético. Utiliza-se um modelo de lâmina auroral em que o campo magnético ambiente é considerado localmente homogêneo. O modelo teórico subjacente adotado é o do maser de elétron-cíclotron. O principal resultado obtido revela uma diminuição na ampli cação nal por um fator em torno de três, quando os gradientes dos parâmetros do plasma são considerados explicitamente. Este resultado pode ter implicações na capacidade do maser de elétron-cíclotron em explicar os níveis de radiação mais elevados observados. / The in uence from source region inhomogeneous character on ampli cation of Auroral Kilometric Radiation is investigated. Firstly, a review over relevant works published about the same general theme is made, concerning about observational data as well theoretical models and numerical simulations. This review is preceded by the establishment of de nitions and concepts related to the theme. Two distinct approaches are considered in determining the ampli cation of radiation across the source region. First approach takes the plasma as locally homogeneous, while second approach account, explicitly, for gradients on plasma parameters. The ampli cation is obtained through evaluation of the dielectric tensor and the evolution of radiation through ray tracing. Plasma parameters are obtained using a self-consistent formulation which account for an electric potential drop along geomagnetic eld lines. An auroral slab model is used where the ambient magnetic eld is taken as locally homogeneous. The subjacent theoretical model adopted is the electron-cyclotron maser. The main result obtained reveals a reduction on nal ampli cation by a factor about three, when plasma parameters gradients are explicitly accounted. This nding may have implications on capability of electron-cyclotron maser for explanation the most intense levels of radiation observed.

A in uência do caráter inomogêneo da região-fonte na ampli cação da Radiação Quilom étrica das Auroras é investigada. Inicialmente é feita uma revisão de trabalhos relevantes publicados a respeito do mesmo tema geral, tanto os que concernem aos dados observacionais como os que concernem aos modelos teóricos e simulações numéricas. Esta revisão é precedida pelo estabelecimento de conceitos e de nições pertinentes ao tema. São consideradas duas abordagens distintas na determinação da ampli cação da radiação na região-fonte. A primeira considera o plasma localmente homogêneo, enquanto a segunda toma em conta, explicitamente, a contribuição dos gradientes dos parâmetros do plasma. A ampli cação da radiação é determinada pela avaliação do tensor dielétrico do plasma e pela evolução da radia ção através do estudo de traçado de raios. Os parâmetros do plasma são obtidos através de uma formulação autoconsistente que toma em conta uma queda de potencial elétrico ao longo das linhas de campo geomagnético. Utiliza-se um modelo de lâmina auroral em que o campo magnético ambiente é considerado localmente homogêneo. O modelo teórico subjacente adotado é o do maser de elétron-cíclotron. O principal resultado obtido revela uma diminuição na ampli cação nal por um fator em torno de três, quando os gradientes dos parâmetros do plasma são considerados explicitamente. Este resultado pode ter implicações na capacidade do maser de elétron-cíclotron em explicar os níveis de radiação mais elevados observados. / The in uence from source region inhomogeneous character on ampli cation of Auroral Kilometric Radiation is investigated. Firstly, a review over relevant works published about the same general theme is made, concerning about observational data as well theoretical models and numerical simulations. This review is preceded by the establishment of de nitions and concepts related to the theme. Two distinct approaches are considered in determining the ampli cation of radiation across the source region. First approach takes the plasma as locally homogeneous, while second approach account, explicitly, for gradients on plasma parameters. The ampli cation is obtained through evaluation of the dielectric tensor and the evolution of radiation through ray tracing. Plasma parameters are obtained using a self-consistent formulation which account for an electric potential drop along geomagnetic eld lines. An auroral slab model is used where the ambient magnetic eld is taken as locally homogeneous. The subjacent theoretical model adopted is the electron-cyclotron maser. The main result obtained reveals a reduction on nal ampli cation by a factor about three, when plasma parameters gradients are explicitly accounted. This nding may have implications on capability of electron-cyclotron maser for explanation the most intense levels of radiation observed.

Abstract This thesis studies the ionospheres of the Earth and Mars by combining the observations of versatile instruments providing information on various aspects of the planetary environments. The work on the terrestrial ionosphere focuses particularly on solar wind–magnetosphere–ionosphere coupling, while the work on the Martian ionosphere is based on the development of a new approach to analyse radio-occultation data to retrieve the atmospheric and ionospheric profiles. In the Earth's ionosphere, two papers study the effects of solar wind high-speed streams on the ionospheric F-region peak electron density and on cosmic noise absorption resulting from the precipitation of energetic (>30 keV) electrons into the D region. For the first paper, a modified version of the superposed epoch analysis method, called phase-locked superposed epoch analysis method, was developed. The main finding is that a depletion near the F-region peak takes place in the afternoon and evening sectors during high-speed stream events. This could be explained by an increase in the electron loss rate as a consequence of ion-neutral frictional heating, which enhances the ion temperature and leads to neutral atmosphere expansion. In addition, dayside and post-midnight F-peak electron density increases are observed, probably related to soft particle precipitation. The second study reveals that cosmic noise absorption occurs during up to 4 days after the arrival of a high-speed stream, as substorm-injected energetic electrons precipitate in the midnight to early-afternoon ionosphere, principally at auroral latitudes. A third study reports for the first time observations of a modulation of cosmic noise absorption at periods near 10 s, associated with pulsating aurora. This suggests that the energetic component of the precipitating ux is modulated consistently with the auroral (1–10 keV) energies. At Mars, radio-occultation experiments have been performed by the Mars Express spacecraft since 2004. In this thesis, a new data analysis approach is developed, based on the numerical simulation of radio wave propagation through modelled Martian atmosphere and ionosphere. This approach enables one to overcome limitations inherent in the classical inversion method which has been in use so far. It also gives access to new parameters such as ion density profiles. The new method is tested by analysing the data from two radio-occultation experiments. / Tiivistelmä Tämä väitöskirja tutkii Maapallon ja Marsin ionosfäärejä yhdistämällä useiden eri instrumenttien havaintoja, joilla saadaan tietoa planeettojen ympäristöistä. Maapallon ionosfääriä koskeva työ tutkii aurinkotuuli–magnetosfääri–ionosfäärikytkentää, kun taas Marsin ionosfääriä koskevan työn tavoite on uuden radio-okkultaatiomittauksen data-analyysimenetelmän kehittäminen, joka tuottaa ilmakehän ja ionosfäärin profiileja. Maan ionosfäärin tapauksessa yhdessä julkaisussa tutkitaan nopeiden aurinkotuulivirtausten vaikutuksia F-kerroksen elektronitiheyteen ja toisessa julkaisussa tutkitaan energeettisten (>30 keV) elektronien sateesta johtuvaa kosmisen radiokohinan absorptiota D-kerroksessa. Ensimmäisessä julkaisussa on kehitetty uusi versio data-analyysimenetelmästä, jota kutsutaan vaihelukituksi epookkien superpositiomenetelmäksi. Julkaisun päätulos on, että nopeiden aurinkotuulivirtausten aikana F-kerroksen maksimielektronitiheys pienenee iltapäivän ja illan sektoreilla. Tämä voidaan selittää johtuvan siitä, että ioni-neutraalitörmäysten synnyttämä kitkalämpö kasvattaa ionilämpötilaa ja aiheuttaa lisäksi ilmakehän laajenemisen. Molemmat prosessit kasvattavat elektronien häviönopeutta. F-kerroksen elektronitiheysmaksimi puolestaan kasvaa sektorilla, joka ulottuu keskiyöstä aamun kautta keskipäivään, ja tämä johtuu matalaenergeettisestä elektronisateesta. Toisessa julkaisussa havaitaan, että lisääntynyt kosmisen radiokohinan absorptio kestää jopa neljä päivää nopean aurinkotuulivirtauksen saavuttua Maan kohdalle. Tämä johtuu siitä, että alimyrskyitse injektoidut energeettiset elektronit satavat keskiyön ja aamun ionosfääriin, pääasiassa revontuliovaalin alueella. Kolmas julkaisu raportoi ensimmäistä kertaa havainnon sykkiviin revontuliin liittyvästä kosmisen radiokohinan absorptiosta n. 10 s jaksollisuudella. Tämä osoittaa, että elektronivuon energeettinen komponentti on moduloitu samalla jaksollisuudella kuin revontulielektronien energiat (1–10 keV). Marsissa on tehty radio-okkultaatiomittauksia vuodesta 2004 saakka Mars Express -luotaimen avulla. Vaitoskirjassa on kehitetty uusi datan analyysimenetelmä, joka perustuu numeeriseen simulointiin radioaaltojen etenemisestä Marsin ilmakehässä ja ionosfäärissä. Tämän lähestymistavan avulla vältetään tähän asti käytetyn klassisen inversiomenetelmän rajoitukset. Lisäksi menetelmä tuottaa uusia parametrejä kuten ionitiheysprofiileja. Uutta menetelmää testattiin tulkiten kahden radio-okkultaatiomittauksen aineistoa. / Résumé Le travail présenté dans ce manuscrit de thèse s'articule autour de l'étude des ionosphères terrestre et martienne. Une approche multi-instrumentale est adoptée afin de combiner des observations permettant de mettre en perspective des manifestations de phénomènes physiques de natures différentes mais intervenant dans un même contexte global. Le travail doctoral comporte également un volet modélisation. Le manuscrit de thèse consiste en une partie introductrice à laquelle sont adossées cinq publications dans des revues scientifiques à comité de lecture. La partie introductrice de ce manuscrit de thèse a pour objectif de présenter le contexte scientifique sur lequel est basé le travail doctoral. Un premier chapitre passe en revue les principaux aspects théoriques dans lesquels s'inscrivent les études dont les résultats sont publiés dans les cinq articles. Les atmosphères et ionosphères de la Terre et de Mars y sont succinctement décrites, de même que les interactions entre ces planètes et le vent solaire, comprenant notamment la formation de magnétosphères. Les deux chapitres suivants présentent les instruments dont sont issues les données utilisées dans ce travail doctoral ainsi que les méthodes d'analyse des données. Le quatrième chapitre résume les principaux résultats obtenus autour des trois grandes thématiques abordées au cours de cette thèse. Enfin, des pistes quant à la continuation potentielle du travail présenté dans ce manuscrit de thèse sont évoquées en conclusion. Le premier article porte sur une étude statistique des effets des courants de vent solaire rapide sur la région F de l'ionosphère aurorale. Il s'appuie sur des données mesurées par l'ionosonde de Sodankylä entre 2006 et 2008. Au cours de cette période, 95 événements associés à des courants de vent solaire rapide ont été sélectionnés, et la réponse de l'ionosphère au-dessus de Sodankylä a été étudiée à partir des fréquences critiques des régions E et F de l'ionosphère, qui donnent la valeur du pic de concentration électronique dans ces deux régions. Pour cela, une version modifiée de la méthode des époques superposées a été développée, appelée “méthode des époques superposées avec verrouillage de phase”. Une augmentation du pic de concentration des régions E et F est observée du côté nuit et le matin, en lien avec une activité aurorale accrue, tandis qu'une déplétion de la région F est révélée aux temps magnétiques locaux situés entre 12 h et 23 h. Une estimation des effets d'une possible modification de l'équilibre photo-chimique résultant d'un accroissement du chauffage issu de la friction entre les ions et les éléments neutres est proposée. Le deuxième article s'intéresse aux précipitations énergétiques dans l'ionosphère aurorale durant ces mêmes 95 événements, en étudiant l'absorption du bruit cosmique qui en résulte. Il apparaît que les événements au cours desquels le vent solaire demeure rapide pendant plusieurs jours produisent davantage de précipitations énergétiques, qui peuvent atteindre les latitudes subaurorales. Par ailleurs, trois types de précipitations énergétiques sont étudiés séparément, selon qu'elles sont associées avec des signatures de sous-orage magnétique, avec des pulsations géomagnétiques, ou ni l'un ni l'autre. Les deux premiers types de précipitations semblent liés. En effet, l'analyse des données suggère que les électrons énergétiques sont injectés dans la magnétosphère interne durant les sous-orages. Tandis qu'une partie d'entre eux précipitent immédiatement du côté nuit, d'autres dérivent vers le côté matin, où ils subissent des interactions avec des ondes électromagnétiques de type siffleur (whistler en anglais), qui peuvent être modulées par des pulsations géomagnétiques, menant à leur précipitation. Le troisième article présente pour la première fois l'observation de signatures d'aurore pulsante dans des données d'absorption du bruit cosmique. Ces signatures sont consistantes avec les pulsations observables dans l'émission aurorale, et semblent indiquer une modulation cohérente des composantes aurorale (1–10 keV) et énergétique (> 30 keV) du spectre des précipitations électroniques au cours d'une aurore pulsante. Le quatrième article introduit une nouvelle méthode proposée pour analyser les données de radio-occultation mesurées par la sonde Mars Express. Cette approche vise à contourner des difficultés posées par les hypothèses fortes nécessaires à la mise en œuvre de la méthode classique d'inversion, notamment celle d'un environnement martien à symétrie sphérique — qui n'est pas acceptable lors de sondages proches du terminateur jour-nuit. La nouvelle méthode est basée sur la modélisation de l'atmosphère et de l'ionosphère de Mars, et sur la simulation de la propagation des ondes radio entre la station sol sur Terre et Mars Express lors d'une expérience de radio-occultation. Les paramètres libres contrôlant les profils atmosphériques et ionosphériques sont ajustés afin que la simulation reproduise le plus fidèlement possible les mesures. Le cinquième article est une réponse à un commentaire sur l'article précédent. Il vise d'une part à répondre aux critiques émises sur la méthode développée, montrant que celles-ci n'en remettent en cause ni la validité ni la pertinence, et d'autre part à y apporter quelques améliorations.

The goal of this thesis is to improve our knowledge on energetic particle precipitation into the Earth’s atmosphere from the thermosphere to the surface. The particles origin from the Sun or from temporarily trapped populations inside the magnetosphere. The best documented influence of solar (high-) energetic particles on the atmosphere is the Ozone depletion in high latitudes, attributed to the generation of HOx and NOx by precipitating particles (Crutzen et al., 1975; Solomon et al., 1981; Reid et al., 1991). In addition Callis et al. (1996b, 2001) and Randall et al. (2005, 2006) point out the importance of low-energetic precipitating particles of magnetospheric origin, creating NOx in the lower thermosphere, which may be transported downwards where it also contributes to Ozone depletion. The incoming particle flux is dramatically changing as a function of auroral/geomagnetical activity and in particular during solar particle events. As a result, the degree of ionization and the chemical composition of the atmosphere are substantially affected by the state of the Sun. Therefore the direct energetic or dynamical influences of ions on the upper atmosphere depend on solar variability at different time scales. Influences on chemistry have been considered so far with simplified precipitation patterns, limited energy range and restrictions to certain particle species, see e.g. Jackman et al. (2000); Sinnhuber et al. (2003b, for solar energetic protons and no spatial differentiation), and Callis et al. (1996b, 2001, for magnetospheric electrons only). A comprehensive atmospheric ionization model with spatially resolved particle precipitation including a wide energy range and all main particle species as well as a dynamic magnetosphere was missing. In the scope of this work, a 3-D precipitation model of solar and magnetospheric particles has been developed. Temporal as well as spatial ionization patterns will be discussed. Apart from that, the ionization data are used in different climate models, allowing (a) simulations of NOx and HOx formation and transport, (b) comparisons to incoherent scatter radar measurements and (c) inter-comparison of the chemistry part in different models and comparison of model results to MIPAS observations. In a bigger scope the ionization data may be used to better constrain the natural sources of climate change or consequences for atmospheric dynamics due to local temperature changes by precipitating particles and their implications for chemistry. Thus the influence of precipitating energetic particles on the composition and dynamics of the atmosphere is a challenging issue in climate modeling. The ionization data is available online and can be adopted automatically to any user specific model grid.