京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19091号 / エネ博第315号 / 新制||エネ||64(附属図書館) / 32042 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 岸本 泰明, 教授 前川 孝, 教授 中村 祐司 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19503号 / 理博第4163号 / 新制||理||1598(附属図書館) / 32539 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 柴田 一成, 教授 一本 潔, 教授 嶺重 慎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20181号 / 理博第4266号 / 新制||理||1613(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)教授 柴田 一成, 教授 一本 潔, 准教授 浅井 歩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20184号 / 理博第4269号 / 新制||理||1613(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田口 聡, 教授 家森 俊彦, 教授 塩谷 雅人 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The ionosphere carries a substantial portion of the electrical current flowing in Earth's space environment. Currents and electric fields in the ionosphere are generated through (1) the interaction of the solar wind with the magnetosphere, i.e. magnetic reconnection and (2) the collision of neutral molecules with ions leading to charged particle motions across the geomagnetic field, i.e. neutral wind dynamo. In this study we applied statistical and deep learning techniques to various datasets to investigate the driving influences of ionospheric electrodynamics at mid- and high-latitudes. In Chapter 2, we analyzed an interval on 12 September 2014 which provided a rare opportunity to examine dynamic variations in the dayside convection throat measured by the RISR-N radar as the IMF transitioned from strong By+ to strong Bz+. We found that the high-latitude plasma convection can have dual flow responses with different lag times to strong dynamic IMF conditions that involve IMF By rotation. We proposed a dual reconnection scenario, one poleward of the cusp and the other at the magnetopause nose, to explain the observed flow behavior. In Chapters 3 and 4, we investigated the driving influences of nightside subauroral convection. We developed new statistical models of nightside subauroral (52 - 60 degree) convection under quiet (Kp <= 2+) to moderately disturbed (Kp = 3) conditions using data from six mid-latitude SuperDARN radars across the continential United States. Our analysis suggests that the quiet-time subauroral flows are due to the combined effects of solar wind-magnetosphere coupling leading to penetration electric field and neutral wind dynamo with the ionospheric conductivity modulating their relative dominance. In Chapter 5, we examined the external drivers of magnetic substorms using machine learning. We presented the first deep learning based approach to directly predict the onset of a magnetic substorm. The model has been trained and tested on a comprehensive list of onsets compiled between 1997 and 2017 and achieves 72 +/- 2% precision and 77 +/- 4% recall rates. Our analysis revealed that the external factors, such as the solar wind and IMF, alone are not sufficient to forecast all substorms, and preconditioning of the magnetotail may be an important factor. / Doctor of Philosophy / The Earth's ionosphere, ranging from about 60 km to 1000 km in altitude, is an electrically conducting region of the upper atmosphere that exists primarily due to ionization by solar ultraviolet radiation. The Earth's magnetosphere is the region of space surrounding the Earth that is dominated by the Earth's magnetic field. The magnetosphere and ionosphere are tightly coupled to each other through the magnetic field lines which act as highly conductive wires. The sun constantly releases a stream of plasma (i.e., gases of ions and free electrons) known as the solar wind, which carries the solar magnetic field known as the interplanetary magnetic field (IMF). The solar wind interacts with the Earth's magnetosphere and ionosphere through a process called magnetic reconnection, which drives currents and electric fields in the coupled magnetosphere and ionosphere. The ionosphere carries a substantial portion of the electrical currents flowing in the Earth's space environment. The interaction of the ionospheric currents and electric fields with plasma and neutral particles is called ionospheric electrodynamics. In this study we utilized statistical and machine learning techniques to study ionospheric electrodynamics in three distinct regions. First, we studied the influence of duskward IMF on plasma convection in the polar region using measurements from the Resolute Bay Incoherent Scatter Radar – North (RISR-N). Specifically, we analyzed an interval on Sep. 12, 2014 when the RISR-N radar made measurements in the high latitude noon sector while the IMF turned from duskward to strongly northward. We found that the high latitude plasma convection can have flow responses with different lag times during strong IMF conditions that involve IMF By rotation. Such phenomena are rarely observed and are not predicted by the antiparallel or the component reconnection models applied to quasi‐static conditions. We propose a dual reconnection scenario, with reconnection occurring poleward of the cusp and also at the dayside subsolar point on the magnetopause, to explain the rarely observed flow behavior. Next, we used measurements from six mid-latitude Super Dual Auroral Radar Network (SuperDARN) radars distributed across the continental United States to investigate the driving influences of plasma convection in the subauroral region, which is equatorward of the region where aurora is normally observed. Previous studies have suggested that plasma motions in the subaruroral region were mainly due to the neutral winds blowing the ions, i.e. the neutral wind dynamo. However, our analysis suggests that subauroral plasma flows are due to the combined effects of solar wind-magnetosphere coupling and neutral wind dynamo with the ionospheric conductivity modulating their relative importance. Finally, we utilized the latest machine learning techniques to examine the external drivers (i.e., solar wind and IMF) of magnetic substorms, which is a physical phenomenon that occurs in the auroral region and causes explosive brightening of the aurora. We developed the first machine learning model that forecasts the onset of a magnetic substorm over the next one hour. The model has been trained and tested on a comprehensive list of onsets compiled between 1997 and 2017 and correctly identify substorm onset ~75% of the time. In contrast, an earlier prediction algorithm correctly identified only ~21% of the substorm onsets in the same dataset. Our analysis revealed that external factors alone are not sufficient to forecast all substorms, and preconditioning of the nightside magnetosphere may be an important factor.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

Interpretation has the potential to play an important role in involving the general public in the dialogue about sustainability, and what this may mean for the future of humans on the earth. Yet interpreters often fail to address this issue. In fact, it can be argued that much interpretation fails to truly engage its audiences or provoke serious thought about our relationship with the rest of nature or our future lifestyles. How can interpretation be made more engaging and provocative, and contribute to the dialogue about sustainability? How can it reach this potential? Some educators and interpreters advocate the use of drama to help people connect with natural and cultural heritage. Powerful dramatic experiences can become embedded in the emotions and leave enduring impressions. Drama is used as an educational tool around the world. Can it be used by interpreters to expand visitors’ conceptions of the human-nature culture milieu? This study addresses the paucity of empirical evidence regarding the effectiveness of dramatized interpretation. Ten practitioners of dramatized interpretation were interviewed to explore the current use of drama in interpretation in Queensland, Australia, and in particular, the practitioners’ perceptions of these practices and their effectiveness. Current practice was evaluated according to the drama, interpretation and education literature, particularly recent theoretical developments. Practitioners displayed a strong understanding of the importance of engagement in interpretation, using a variety of drama forms and strategies to create resonant experiences and strengthen visitors’ connections with natural, historic and cultural heritage. In addition, they designed their programs to provoke thought and foster deep understanding of environmental and conservation issues, and obtained evidence of provocation and conceptual enhancement. Notwithstanding this, it is concluded that dramatized interpretation could have a greater impact on conceptual enhancement if practitioners designed their programs according to constructivist, group learning and sociocultural perspectives. Practitioners could also make a greater contribution to general environmental education if they explicitly addressed the issue of sustainability, using drama to tell stories that encapsulate the concept of sustainability and provide a vision of sustainable living. A checklist is provided to assist practitioners in the design and evaluation of dramatized programs. Recommendations are also given for interpreters wishing to explore the application of drama to their interpretive setting.

L'objectif de cette thèse est l'étude de la reconnexion magnétique dans les plasmas non-collisionels et relativistes. De tels plasmas sont présents dans divers objets astrophysiques (MQs, AGNs, GRBs...), où la reconnexion pourrait expliquer la production de particules et de radiation de haute énergie, un chauffage, ou des jets. Une compréhension fondamentale de la reconnexion n'est cependant toujours pas acquise, en particulier dans les plasmas relativistes ion-électron. Nous présentons d'abord les bases de la reconnexion magnétique. Nous démontrons des résultats particuliers à la physique des plasmas relativistes, concernant par exemple la distribution de Maxwell-Jüttner. Ensuite, nous réalisons une étude détaillée de l'outil numérique utilisé : les simulations particle-in-cell (PIC). Le fait que le plasma réel contienne beaucoup plus de particules que le plasma PIC a des conséquences importantes (collisionalité, relaxation, bruit) que nous décrivons. Enfin, nous étudions la reconnexion magnétique dans les plasmas ion-électron et relativistes à l'aide de simulations PIC. Nous soulignons des points spécifiques : loi d'Ohm (l'inertie de bulk dominante), zone de diffusion, taux de reconnexion (et sa normalisation relativiste). Les ions et les électrons produisent des lois de puissance, avec un index qui dépend de la vitesse d'Alfvén et de la magnétisation, et qui peut être plus dur que dans le cas des chocs non-collisionels. De plus, les ions peuvent avoir plus ou moins d'énergie que les électrons selon la valeur du champ guide. Ces résultats fournissent une base solide à des modèles d'objets astrophysiques qui, jusque là, supposaient a priori ces résultats. / The purpose of this thesis is to study magnetic reconnection in collisionless and relativistic plasmas. Such plasmas can be encountered in various astrophysical objects (microquasars, AGNs, GRBs...), where reconnection could explain high-energy particle and photon production, plasma heating, or transient large-scale outflows. However, a first principle understanding of reconnection is still lacking, especially in relativistic ion-electron plasmas. We first present the basis of reconnection physics. We derive results relevant to relativistic plasma physics, including properties of the Maxwell-Jüttner distribution. Then, we provide a detailed study of our numerical tool, particle-in-cell simulations (PIC). The fact that the real plasma contains far less particles than the PIC plasma has important consequences concerning relaxation times or noise, that we describe. Finally, we study relativistic reconnection in ion-electron plasmas with PIC simulations. We stress outstanding properties: Ohm's law (dominated by bulk inertia), structure of the diffusion zone, energy content of the outflows (thermally dominated), reconnection rate (and its relativistic normalization). Ions and electrons produce power law distributions, with indexes that depend on the inflow Alfvén speed and on the magnetization of the corresponding species. They can be harder than those produced by collisionless shocks. Also, ions can get more or less energy than the electrons, depending on the guide field strength. These results provide a solid ground for astrophysical models that, up to now, assumed with no prior justification the existence of such distributions or of such ion/electron energy repartition.

La reconnexion magnétique est un mécanisme fondamental de conversion d'énergie dans le plasma. Il se déroule dans les régions minces de fort courant appelées couches de courants, et produit le chauffage et l accélération des particules. Dans un milieu turbulent, la reconnexion magnétique a été observée dans de petites structures qui se forment dans celui-ci, et on a postulé que cela contribue de façon importante la dissipation de l'énergie turbulente l'échelle cinétique. Pour ce travail, nous examinons les données des satellites Custer dans la magnétogaine de la Terre, en aval du choc quasi-parallèle. La détection des couches de courant d'échelle ionique a été réalisé par l'application de la méthode de la variance partielle des incréments (PVI) pour des satellites multiples. Les proprietées des couches de courant observées étaient différentes pour des valeurs de l'indice PVI élevées(PV I > 3) et bas (PV I < 3). Nous avons observé une population distincte de haut indice PVI (> 3) structures qui représentaient ~ 20% du total. Ces couches de courant ont une rotation du champ magnétique élevée (> 90o). Afin d'estimer le chauffage local survenant dans ces couches de courant, une estimation de la température des électrons a été obtenue à haute résolution temporelle (125ms) parles distributions d'électrons partielles mesurées par Cluster. Cela a permis pour la première fois d'étudier le chauffage d'électrons localisés dans les couches de courant d'échelle ionique. L'augmentation observée de la température des électrons estimée dans les couches de courant aux PVI élevées suggèrent qu'ils sont importants pour le chauffage local d'électrons et de dissipation d'énergie. Nous avons également examiné les mesures l'intérieur de la région de diffusion d'une couche de courant o la reconnexion magnétique est en cours. Les observations simultanées par des satellites multiples permettent aussi d'étudier les distributions d'électrons et l'activité des ondes à des distances différentes de la ligne x. Des différences significatives ont été observées dans les populations d'électrons comme ils ont été chauffés en passant par la couche de courant. En particulier, les électrons sont chauffés dans la direction parallèle au champ magnétique proximité de la ligne x, alors qu'aucune variation significative n'a été observée dans la direction perpendiculaire. Cependant,la distribution est plus isotrope en aval de la ligne x, chauffées par des électrons dans la direction perpendiculaire. / Magnetic reconnection is a fundamental energy conversion process in plasma. It occurs in thin regions of strong current known as current sheets and results in particle heating and acceleration. In turbulence, which is ubiquitous in space plasma, magnetic reconnection has been observed to occur in small scale structures that form therein, and is thought to contribute to dissipation of turbulent energy at kinetic scales. For this work we examine data from the Cluster spacecraft in the Earth's magnetosheath, downstream of the quasi-parallel shock. The detection of ion-scale current sheets was performed by implementing the PartialVariance of Increments (PVI) method for multiple spacecraft. The properties of the observed current sheets were different for high (> 3) and low (< 3) values of the PVI index. We observed a distinct population of high PVI (> 3) structures that accounted for ~ 20% of the total. Those current sheets have high magneticshear (> 90degrees). In order to estimate the local heating occurring within those current sheets, a proxy of the electron temperature was obtained at high time resolution(125ms) from the partial distributions measured by Cluster. This allowed for the first time to study the localized electron heating within ion-scale currentsheets. The observed enhancement of the estimated electron temperature withinthe high PVI current sheets suggest that they are important for local electron heating and energy dissipation. We also examined measurements inside the diffusion region of a thin reconnecting current sheet. Multi-spacecraft observationsallow as to study electron distributions and wave activity at different distances from the x-line. Significant differences were observed in the electron populations as they were heated going through the current sheet. In particular electrons were heated in the direction parallel to the magnetic field in close proximity to thex-line, whereas no significant variation was observed in the perpendicular direction. However, the distribution was more isotropic downstream of the x-line with electrons heated in the perpendicular direction.