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Theses

Injection de flux et d'hélicité magnétiques dans l'atmosphère solaire

Abstract : This thesis is related to the mechanisms of emergence into the solar atmosphere, of two quantities playing key roles in solar activity: magnetic flux and magnetic helicity. Helicity, which is a topological measure of twist and shear, is believed to be a conserved quantity for solar conditions, in the frame of magnetohydrodynamics (MHD). A crucial phase in the emergence process of these quantities, which are generated and amplified in the solar interior, are their injection through the solar photosphere, the transition region between the solar interior and atmosphere.
The first part of my work provided new answers to questions unsolved by the classical scenario of emergence. I have analyzed multi-wavelength observations (FGE, TRACE, SoHO, THEMIS) of an emerging active region. I demonstrated that magnetic flux tubes emerge with a flat undulated shape and that small scale magnetic reconnection events, are necessary to this emergence process. Then, using a 3D MHD numerical simulation, I studied the mechanism of magnetic reconnection and in particular the natural formation of current layers where regions of strong variations of magnetic connectivity, called quasi-separatrix layers, are present. Finally, I demonstrated that the classical definition of helicity flux density is biased and proposed a more accurate definition. I applied my new definition to observations of active regions and showed that the photospheric injection pattern of magnetic helicity is unipolar and homogenous.
This study allows to link the generation of helicity in the solar atmosphere, its injection and its distribution in the solar corona and its ejection in the interplanetary medium.
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https://tel.archives-ouvertes.fr/tel-00108682
Contributor : Etienne Pariat <>
Submitted on : Monday, October 23, 2006 - 9:29:06 AM
Last modification on : Thursday, December 10, 2020 - 11:09:08 AM
Long-term archiving on: : Friday, November 25, 2016 - 1:59:51 PM

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  • HAL Id : tel-00108682, version 1

Citation

Etienne Pariat. Injection de flux et d'hélicité magnétiques dans l'atmosphère solaire. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2006. Français. ⟨tel-00108682⟩

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