Propriétés magnétiques des structures éruptives solaires

Abstract : Solar eruptions constitute the most energetic phenomena of the solar system. In a few tens of minutes, an energy comparable to hundred thousand times the annual world human energy consumption is released in the solar atmosphere. During these events, magnetized matter, as well as energetic particles and radiations, are ejected toward the interplanetary space and frequently interact with the Earth magnetic environment. For our society, which relies more and more on technologies, the impact of these eruptions is becoming an ever-increasing concern, requiring us to learn how to guard against their detrimental effects. Solar eruption prediction, within the scope of the emerging applied discipline of space weather, requires to understand the physical mechanisms that generates these eruptions. The work presented in this thesis corresponds to fundamental researches in physics of the Sun-Earth relations. The overall objective targets the development of new tools to forecast solar activity. The framework of study of these phenomena is magnetohydrodynamics, the physical paradigm adapted to the study of the hot magnetized plasma that constitutes the solar atmosphere. The present studies focus on analyzing the properties of the source regions of the eruptions, the solar active regions, which main visible counterpart are the solar sunspots. These active regions correspond to intense concentrations of magnetic fields, which constitutes the energy source that fuels the eruptions. Understanding the trigger of solar eruption thus relies on the determination of the magnetic properties of the active regions. The research methodology that is employed is based on close and synergistic combination of different means of investigation; analytical theory, conceptual modeling, numerical experimentation, and multi-wavelength multi-instrument observational analysis. Thanks to these methods, several fundamental quantities and physical properties are being studied: the very magnetic field, its topology and its structuration in potential and non-potential fields, the associated energies, the induced electric currents, and finally magnetic helicity, an underrated quantity up to now. Through the synthesis of about sixty scientific studies, this thesis intends to demonstrate that, while each quantity provides distinct information, these are complementary and enables a global description of eruptive magnetic fields, allowing the creation of an actual 3D standard model for solar eruptions. Regarding solar eruptions prediction, the studies on the theory of the measurement of magnetic helicity, now allow to truly and correctly estimate this quantity and determine its link with eruptivity. Preliminary studies of numerical experiments show that magnetic helicity could be the ground base of efficient diagnostics of the eruptive state of solar active regions.
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Etienne Pariat. Propriétés magnétiques des structures éruptives solaires. Astrophysique stellaire et solaire [astro-ph.SR]. Observatoire de Paris; Paris Sciences et Lettres, 2019. ⟨tel-02153222⟩

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