学位プログラム名: 京都大学大学院思修館 / 京都大学 / 新制・課程博士 / 博士(総合学術) / 甲第23343号 / 総総博第16号 / 新制||総総||3(附属図書館) / 京都大学大学院総合生存学館総合生存学専攻 / (主査)教授 山敷 庸亮, 教授 寶 馨, 准教授 浅井 歩 / 学位規則第4条第1項該当 / Doctor of Philosophy / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24414号 / 理博第4913号 / 新制||理||1702(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 浅井 歩, 教授 一本 潔, 教授 横山 央明 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This thesis considers the magnetic topology of the global solar corona. To understand the magnetic topology we use the magnetic skeleton which provides us with a robust description of the magnetic field. To do this we use a Potential Field model extrapolated from observations of the photospheric magnetic field. Various measurements of the photospheric magnetic field are used from both ground-based observatories (Kitt-Peak and SOLIS) and space-based observatories (MDI and HMI). Using the magnetic skeleton we characterise particular topological structures and discuss their variations throughout the solar cycle. We find that, from the topology, there are two types of solar minimum magnetic field and one type of solar maximum. The global structure of the coronal magnetic field depends on the relative strengths of the polar fields and the low-latitude fields. During a strong solar dipole minimum the heliospheric current sheet sits near the equator and the heliospheric current sheet curtains enclose a large amount of mixed polarity field which is associated with many low-altitude null points. In a weak solar dipole minimum the heliospheric current sheet becomes warped and large scale topological features can form that are associated with weak magnetic field regions. At solar maximum the heliospheric current sheet is highly warped and there are more null points at high altitudes than at solar minimum. The number of null points in a magnetic field can be seen as a measure of the complexity of the field so this is investigated. We find that the number of nulls above 10Mm falls off with height as a power law whose slope depends on the phase of the solar cycle. We compare the magnetic topology we found at particular times with observations of the Doppler velocity and intensity around particular active regions to see if it is possible to determine whether plasma upflows at the edge of active regions are linked to open field regions.

L’origine et l’évolution des différentes structures qui peuplent l’au-delà de la photosphère du Soleil, ainsi que les processus qui interviennent dans la dynamique et le chauffage de sa couronne demeurent de nos jours assez peu compris. L’inextricable complexité inhérente aux phénomènes physiques qui gouvernent l’atmosphère externe solaire s’accompagne de l’absence de données adaptées au besoin scientifique. En effet, l’interprétation et la modélisation des « mécanismes » qui raccordent les échanges entre la chromosphère et la couronne dépendent de paramètres d’observation critiques. Il est par exemple essentiel de pouvoir mesurer de larges bandes de températures et densités verticales s’adaptant aux multiples échelles spatiales et temporelles caractéristiques des différents évènements qui se déroulent dans le Soleil. La compréhension de la dynamique des plasmas repose aussi sur l’analyse Doppler de la scène observée. Ceci implique notamment la capacité de combiner des techniques de spectroscopie et d’imagerie simultanément dans le temps. Pour la couronne, le passage à l’UV spatial est incontournable, et relève d’un véritable défi technique. Malgré les excellents progrès technologiques, l’étude UV du Soleil est une science relativement récente, et aucune mission spatiale solaire n’a pu fournir jusqu’à présent une spectro-imagerie combinée et simultanée dans le domaine spectral qui nous intéresse. C’est pour répondre à cette attente que l’étude d’un nouveau dispositif appelé IFTSUV (abréviation de Imaging Fourier Transform Spectrometer working in the far UV), est présentée dans cette recherche. Malgré l’absence de missions d’opportunité dans l’horizon proche, les travaux de thèse se sont déroulés suivant le plan de l’action R&T du CNES R-S11/OT-0004-040, concernant la définition d’un spectro-imageur à transformée de Fourier dans l’UV lointain, et la réalisation en laboratoire d’un démonstrateur de métrologie dédié, pierre angulaire de la faisabilité technique de l’instrument. Ainsi, partant de la détermination du besoin scientifique et de la justification du choix technique, le premier objectif de cette étude est de concevoir un modèle instrumental préliminaire complet de l’IFTSUV. La spécification technique est fondée sur le calcul de dimensionnement et l’évaluation théorique des spécifications en termes de précision spectrale, qualité de l’image et rapport signal sur bruit. A travers l’identification des points durs, la réalisation d’une métrologie d’asservissement du miroir d’échantillonnage apparait tout naturellement, comme un besoin intrinsèque de la validation du concept. En effet, l’acquisition de l’interférogramme doit se faire de manière rigoureusement constante et le pas d’échantillonnage doit être connu avec une grande exactitude, car il fixe les nombres d’onde pour lesquels les spectres bruts sont calculés. Le maquettage d’une solution métrologique constitue donc le deuxième objectif de ce travail. L’architecture optique mise en place a été choisie afin de satisfaire les besoins de stabilité angulaire (< 2.5 μrad) et de précision linéaire (< 8 nm) discernés, et testée en laboratoire. Les résultats sur la maquette valident le concept, même si ses performances s’éloignent des prédictions théoriques. L’évaluation expérimentale des performances permet d’établir des solutions aux problèmes rencontrés qui convergent vers l’optimisation et le prototypage d’un système pouvant être intégré dans une application spatiale. / The origin and evolution of the different structures that inhabit beyond the Sun’s photosphere, as well as the processes involved in the dynamics and the heating of the corona remain quite unknown. The inextricable complexity of the physical phenomena that govern the solar outer atmosphere is accompanied by the lack of suitable data adapted to the scientific need. Indeed, the interpretation and the models of the mechanisms that connect the exchanges between the chromosphere and the corona depend on critical observational parameters. It is for example essential to measure broad bands of vertical temperature and density ranges that fit the multiple spatial and temporal scales that are characteristic of the different events that take place in the Sun. The understanding of the dynamics of the plasma must be also based on the Doppler analysis of the observed scene. That implies the ability to combine time resolved spectroscopic and imaging technologies. Moreover, space is the place to observe the far UV corona and that implies a real technical challenge. Despite excellent advances in technology and instrumentation, the study of the Sun in the far UV is a fairly recent. To date, no solar space mission could provide a combined and simultaneous diagnostic of both observable in the spectral range of interest. It is because of these expectations that the study of a new device called IFTSUV (the acronym of Imaging Fourier Transform Spectrometer working in the far UV) is presented in this research. Despite the lack of opportunity missions on the near horizon, these thesis works have been conducted thanks to the R&D funding R-S11/OT-0004-040 from the CNES, concerning either the definition of an imaging Fourier transform spectrometer in the far UV, or the realization of a laboratory metrology demonstrator that is the cornerstone of the instrument’s feasibility. Thus, starting from the definition of the scientific requirements that lead to the technical choice, the first objective of this study is to develop a preliminary instrumental model of the IFTSUV. The overall technical and design specifications are based in theoreticalcalculations that have been expressed in terms of spectral accuracy, image quality and signal to noise ratio. Throughout the identification of difficult points, the realization of a servo-metrology system dedicated to the sampling mirror appears naturally as an intrinsic need of proof of concept. Indeed, the wavenumbers from the raw spectra are set by the interferogram. That implies that acquisition must be rigorously constant and that the sampling steps must be known with high accuracy. The mockup of a metrological solution is therefore the second objective of this work. The optical breadboard architecture under test has been chosen to meet the needs of angular stability (< 2.5 μrad) and linear accuracy (< 8 nm). The results on the demonstrator validate the concept even if its performances are away from the theoretical predictions. The experimental performance evaluation is used to establish solutions to the instrumental problems encountered. That converge to the optimization and prototyping of a system that could be integrated in a space based application.

With  the  continuous  advances  in  microwave  technology,  microwave  components  and  related magnetic materials become more important in industrial environment. In order to further develop the microwave components, it is of interest to find new kinds of technologies and materials. Here, we  introduce  a  new  kind  of  material  --  amorphous  metallic  wires  which  could  be  used  in microwave  components,  and  use  these  wires  to  design  new  kinds  of  attenuators.  Based  on  the fundamental  magnetic  properties  of  amorphous  wires  and  transmission  line  theory,  we  design  a series of experiments focusing on these wires, and analyze all the experimental results.    Experimental  results  show  that  incident  and  reflected  signals  produce  interference  and  generate standing  waves  along  the  wire.  At  given  frequency,  the  insertion  attenuation  S21 [dB]  of  an amorphous wire increases monotonically with dc bias current. The glass cover will influence the  magnetic  domain  structure  in  amorphous  metallic  wires.  Therefore,  it  will  affect  the circumference  permeability  and  change  the  signal  attenuation.  It  is  necessary  to  achieve  the impedance  matching  by  coupling  to  an  inductor  and  a  capacitor  in  the  circuit.  The  impedance matching  makes  the  load  impedance  close  to  the  characteristic  impedance  of  transmission  line. The magnetic wire-based attenuator designed in this thesis work are characterized and compared to conventional pin-diode attenuator.

Diese Dissertation befasst sich mit Beobachtungen von konvektiven Strömungen in der Sonne, und insbesondere mit den Auswirkungen der Rotation auf diese Strömungen auf der Längenskala von Supergranulation und größeren Skalen (>30 Mm). Die Rotation der Sonne verursacht durch die Corioliskraft Wirbelströmungen und bewirkt anisotrope Korrelationen der Geschwindigkeitskomponenten. Man nimmt an, dass diese Korrelationen die Dynamik der Sonne auf großen Längenskalen beeinflussen. Um horizontale Strömungen zu messen, untersuchen wir photosphärische Aufnahmen der Doppler-Geschwindigkeit und der Kontinuumsintensität des ``Helioseismic and Magnetic Imagers'' (HMI) an Bord der Raumsonde ``Solar Dynamics Observatory'' (SDO) mit Hilfe der Methoden Time-Distance-Helioseismologie (TD) und Local Correlation Tracking (LCT) von Granulen. Im Rahmen der Time-Distance-Helioseismologie kann die lokale vertikale Vortizität gemessen werden, indem die Differenz von Wellenlaufzeiten entlang eines geschlossenen Weges ermittelt wird (Laufzeiten gegen den Uhrzeigersinn minus Laufzeiten im Uhrzeigersinn). Die Ergebnisse von TD und LCT stimmen bis zu den höchsten studierten Breitengraden (+/-60°) hervorragend überein, nachdem eine Korrektur für so genannte Center-to-Limb-Effekte angewandt wurde. Nach dem Mitteln in Ost-West-Richtung messen wir abseits des Äquators eine schwache, aber signifikante Korrelation zwischen der horizontalen Komponente der Divergenz und der vertikalen Komponente der Vortizität von supergranularen Strömungen. Ein Vergleich der Messungen mit einem Modell für das Rauschen offenbart, dass die TD-Methode verwendet werden kann, um die vertikale Vortizität von Strömungen auf Längenskalen größer als 15 Mm zu messen. Damit können mit dieser Methode nicht nur Strömungen in Supergranulen, sondern auch in Riesenzellen gemessen werden. Wir stellen außerdem fest, dass das Signal in Messungen der vertikalen Vortizität mit Hilfe von Aufnahmen von SDO/HMI sehr viel leichter detektiert werden kann als mit Hilfe von früheren Aufnahmen. Um den Einfluss der Sonnenrotation auf die Supergranulation im Detail zu studieren, kartieren wir die vertikale Vortizität der Strömungen in der durchschnittlichen Supergranule. Die durchschnittliche Supergranule wird konstruiert, indem Tausende von einzelnen Supergranulen in einem bestimmten Breitengradbereich durch räumliche Verschiebungen zur Deckung gebracht werden. Damit lösen wir zum ersten Mal die vertikale Vortizität in Aus- und Einströmungen räumlich auf. In nördlichen Breiten sind Ausströmungen im Mittel mit einer Zirkulation im Uhrzeigersinn verbunden. Das Signal verschwindet am Äquator und hat in südlichen Breiten das umgekehrte Vorzeichen. Aus- und Einströmungen besitzen eine vertikale Vortizität mit entgegengesetzten Vorzeichen, wie es von Vorhersagen erwartet wird, die sich auf die Corioliskraft stützen. Es wird offenbar, dass der Vortizitätspeak in der durchschnittlichen supergranularen Ausströmung vergleichsweise ausgedehnt und schwach ist (Halbwertsbreite von 13 Mm und Spitzenwert von 4 x 10^{-6}/s im Uhrzeigersinn bei 40° nördlicher Breite), verglichen mit der durchschnittlichen Einströmung (Halbwertsbreite von 8 Mm und Spitzenwert von 8 x 10^{-6}/s gegen den Uhrzeigersinn). Darüberhinaus untersuchen wir mit SDO/HMI-Daten das Magnetfeld in den Einströmungen um die durchschnittliche Supergranule am Äquator herum. Die mittlere Stärke des Magnetfelds stellt sich als richtungsabhängig heraus: In westlicher Richtung (prograd) ist das Netzwerkfeld ungefähr 10% stärker als in östlicher Richtung. Dieses überraschende Ergebnis fügt dem Rätsel um die Supergranulation einen weiteren Aspekt hinzu. Ob ein Zusammenhang mit anderen bekannten Eigenschaften der Supergranulation besteht (beispielsweise zur Superrotation des supergranularen Strömungsmusters oder zu wellenartigen Eigenschaften), ist nicht geklärt.

The structure of the magnetic field is often an important factor in many energetic processes in the solar corona. To determine the topology of the magnetic field features such as null points, separatrix surfaces, and separators must be found. It has been found that these features may be preferred sites for the formation of current sheets associated with the accumulation of free magnetic energy. Over the last decade, it also became clear that the geometrical analogs of the separatrices, the so-called quasi separatrix layers, have similar properties. This thesis has the aim of investigating these properties and to find correlations between these quantities. Our goal is to determine the relation between the geometrical features associated with the QSLs and with current structures, sites of reconnection and topological features. With these aims we conduct three different studies. First, we investigate a non linear force free magnetic field extrapolation from observed magnetogram data taken during a solar flare eruption concentrating our attention on two snapshots, one before the event and one after. We determine the QSLs and related structures and by considering carefully how these change between the two snapshots we are able to propose a possible scenario for how the flare occurred. In our second project we consider potential source distributions. We take different potential point source models: two four sources models already presented in the literature and a random distribution of fifteen sources. From these potential models we conduct a detailed analysis of the relationship between topological features and QSLs. It is found that the maxima of the Q-factor in the photosphere are located near and above the position of the subphotospheric null points (extending part way along their spines) and that their narrow QSLs are associated with the curves defined by the photospheric endpoints of all fan field lines that start from subphotospheric sources. Our last study investigates two different flux rope emergence simulations. In particular, we take one case with and one without an overlying magnetic field. Here, we can identify the QSLs, current, and sites of reconnection and determine the relation between them. From this work we found that not all high-Q regions are associated with current and/or reconnection and vice-versa. We also investigated the geometry of the field lines associated with high-Q regions to determine which geometrical behaviour of the magnetic field they are associated with. Those that are associated with reconnection also coincide with topological features such as separators.

<div>Planetary rings are, and have been, a common feature throughout the solar system.</div><div>Rings have been observed orbiting each of the giant planets, several Trans-Neptunian Objects, and debris rings are thought to have orbited both Earth and Mars.</div><div>The bright, massive planetary rings orbiting Saturn have been observed for centuries, and the Cassini Mission has given researchers a recent and extensive closeup view of these rings.</div><div>The Saturn ring system has served as a natural laboratory for scientists to understand the dynamics of planetary ring systems, as well as their influence on satellites orbiting nearby.</div><div>Researchers have shown that planetary ring systems and nearby satellites can be tightly-coupled systems.</div><div><br></div><div>In this work, I discuss the physics which dominate the dynamical evolution of planetary ring systems, as well as the interactions with any nearby satellites.</div><div>Many of these dynamics have been incorporated into a one-dimensional mixed Eulerian-Lagrangian numerical model that I call "RING-MOONS," to simulate the long-term evolution of tightly coupled satellite-ring systems.</div><div>In developing RING-MOONS, I have discovered that there are three evolution regimes for tightly-coupled satellite-ring systems which I designate as the "Boomerang," "Torque-Dependent," and "Slingshot" regimes.</div><div>Each regime may be defined using the rotation period of the primary body and the bulk density of the ring material.</div><div><br></div><div>The slow rotation period of Mars places it in the Boomerang regime.</div><div>I hypothesize that a giant impact with Mars ejected material into orbit, forming a debris ring around the planet.</div><div>Using RING-MOONS, I demonstrate how Lindblad torques cause satellites which form at the edge of the ring to initially migrate away from the ring, but over time as the mass of the ring decreases, tidal torques always cause the satellites to migrate inwards.</div><div>Assuming the satellites rapidly tidally disrupt upon migrating to the rigid Roche limit, a new ring is formed.</div><div>I show that debris material cycles between orbiting Mars as a planetary ring, or as discrete satellites, and that Phobos may be a product of a repeated satellite-ring cycle.</div><div>Uranus, which has a faster rotation rate falls within the Torque-Dependent regime.</div><div>Hypothesizing that a massive ring once orbited Uranus, I use RING-MOONS to demonstrate how the satellite Miranda may have formed from such a ring, and migrated outwards to its current orbit, but that any other satellites would have migrated inwards overtime.</div><div><br></div><div>Lastly, I examine Trans-Neptunian Objects (TNOs) in binary systems.</div><div>Tidal torques exerted on each body can decrease the mutual semi-major axis of the system.</div><div>I outline the conditions for which a fully synchronous system may experience a complete decay of the mutual orbit due to tidal torques.</div><div>As the semi-major axis decreases, it is possible for the smaller of the two bodies to shed mass before coming into contact with the more massive to form a contact binary.</div><div>I hypothesize that Chariklo and Chiron are contact binaries that formed via the tidal collapse of a binary TNOs system, and demonstrate how mass shedding may have occurred to form the rings observed today.</div>

We present observational and numerical evidence supporting the theory of impulsive heating of the solar corona. We have run numerical simulations solving the hydrodynamic equations for plasma confined to a magnetic flux tube, for the two distinct cases of steady and impulsive heating. We find that steady heating cannot explain the observed amount of low-temperature plasma in active regions on the sun. The results for impulsive heating closely match those of the observations. The ratio of heating time to cooling time predominantly determines the observed temperature distribution of the plasma. We have also identified an observational bias in calculating intensities of spectral lines in previous studies, which causes an under-estimation of low-temperature plasma. We predict Doppler shifts in the observed line emission that are in agreement with observations, and which may serve as a diagnostic of the strength of heating. We conclude that impulsive heating of active region coronal loops is more likely than steady heating.

L'évolution de notre compréhension des propriétés de la couronne solaire dépend largement de la détermination empirique ou semi-empirique des paramètres fondamentaux du plasma, tels que le champ magnétique, la densité et la température, mais pour lesquels il n'existe pas de mesure directe. L'intégration le long de la ligne de visée complique considérablement l'interprétation des observations, du fait de la superposition de structures aux propriétés physiques différentes. Pour lever cette ambiguïté, on dispose de plusieurs outils, dont la mesure d'émission différentielle (ou DEM; Differential Emission Measure), qui permet d'obtenir la quantité de plasma en fonction de la température le long de la ligne de visée, et la tomographie, qui permet, elle, d'obtenir la distribution spatiale de l'émissivité. Le couplage de ces deux outils permet d'obtenir un diagnostic tridimensionnel en température et densité de la couronne. A l'heure actuelle, le code utilisé dans ce travail est l'un des deux seuls au monde capables de réaliser ce couplage. Cependant, ces deux méthodes requièrent un processus d'inversion, dont les difficultés intrinsèques peuvent fortement limiter l'interprétation des résultats. La méthode développée dans cette thèse s'attache à évaluer la robustesse des diagnostics spectroscopiques par DEM, en proposant une nouvelle technique de caractérisation tenant compte des différentes sources d'incertitudes mises en jeu. En utilisant une approche probabiliste, cette technique permet d'étalonner a priori le problème d'inversion, et ainsi d'étudier son comportement et ses limitations dans le cadre de modèles simples. L'avantage de ce type d'approche est sa capacité à fournir des barres d'erreurs associées aux DEMs reconstruites à partir de données réelles. La technique développée a d'abord été appliquée à l'imageur SDO/AIA dans le cas de modèles de DEMs simples mais capables de représenter une grande variété de conditions physiques au sein de la couronne. Si l'inversion de plasmas proches de l'isothermalité apparaît robuste, nos résultats montrent qu'il n'en va pas de même pour les plasmas largement distribués en température, pour lesquelles les DEMs reconstruites sont à la fois moins précises mais aussi biaisées vers des solutions secondaires particulières. La technique a ensuite été appliquée au spectromètre Hinode/EIS, en utilisant un modèle de DEM représentant la distribution en loi de puissance des DEMs des régions actives, dont la pente permet de fournir des contraintes relatives à la fréquence des événements de chauffage coronal. Nos résultats montrent que les sources d'incertitudes sont à l'heure actuelle trop élevées pour permettre une mesure exploitable de la fréquence. La dernière partie est consacrée aux reconstructions tridimensionnelles obtenues par couplage tomographie/DEM, en s'intéressant aux structures polaires. Premières reconstructions réalisées avec AIA, nos résultats permettent d'étudier l'évolution en température et densité en fonction de l'altitude, montrant la présence de plumes polaires plus chaudes et denses que leur environnement. / Progress in our understanding of the solar corona properties is highly dependant of the emipirical or semi-empirical determination of the plasma fundamental parameters, such as magnetic field, density and temperature. However, there is no direct measurements of such quantities; the integration along the line of sight considerably complicates the interpretations of the observations, due to the superimposition of structures with different properties. To avoid this ambiguity, there exist several tools, including the Differential Emission Measure (DEM) and the tomography reconstruction technique. The former provides the quantity of emitting material as a function of the temperature, whereas the latter is able to reconstruct the three dimensional distribution of the coronal emissivity. Coupling these two techniques leads to a three dimensional diagnostic of the temperature and density. The inversion code used in this work is currently one of the two codes in the world able to perform this coupling. The method described in this work has been developed in order to estimate the robustness of the spectroscopic diagnostics using the DEM formalism, using a new characterisation method taken into account the different uncertainty sources involved in the inversion process. Using a probabilistic approach, this technique is able to calibrate a priori the DEM inversion problem and thus allows to study the inversion behavior and limitations in the context of simple DEMs models. The advantage of this method is its ability to provide confidence level on the reconstructed DEMs computed from real data. First applied to the SDO/AIA (Atmospheric Imaging Assembly) imager in the case of simple models able to represent a variety of plasma conditions, our results show that DEM inversion of isothermal or near-isothermal plasmas is robust, whereas the multithermal solutions are less accurate but also biased to secondary solutions. We also applied the method to the Hinode/EIS (EUV Imaging Spectrometer) spectrometer, using a power law DEM, typical of active regions DEM, from which the slope provides important constraints related to the coronal heating frequency. Our results point out that the different uncertainty sources are currently too high to allow exploitable measurements of this frequency. The last part is dedicated to the three-dimensional reconstructions obtained by coupling tomography and DEM tools, focusing on polar structures. First reconstructions obtained using AIA data, our results allow to study the evolution of the temperature and density as a function of altitude, showing polar plumes denser and hotter than their surrondings.