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Les particules énergétiques solaires : études observationnelles et simulations magnétohydrdynamiques

Abstract : Solar activity manifests itself through highly dynamical events, such as flares and coronal mass ejections, which result in energy release by magnetic reconnection. This PhD focuses on two manifestations of this energy release: solar energetic particles and dynamics of magnetic reconnection. The first part of my work consists in the detailed temporal analyzis of several electromagnetic signatures, produced by energetic particles in the solar atmosphere, with respect to the energetic particle flux at Earth. Using multi-instrument observations, I highlighted that particles can be accelerated by the flare to relativistic energies during a specific episode of acceleration in the impulsive phase. This showed that particles traveled a longer path length than the theoretical length generally assumed. Using in-situ measurements of magnetic field and plasma, I identified the interplanetary magnetic field for 10 particle events, and performing a velocity dispersion analyzis I obtained the interplanetary length traveled by particles. Thanks to the comparison of this two independant studies, I showed that the magnetic structure of the interplanetary medium play a crucial role in the association of the particle flux at Earth and the acceleration signatures of particles at the Sun. The second part of my work focuses on the dynamics of magnetic reconnection. Observationally, the best evidence for magnetic reconnection is the appearance of brigthenings at the solar surface. Performing the first data-driven 3 dimensional magneto-hydrodynamic (MHD) simulation of an observed event, I discovered that the evolution of brightenings can be explained by the succession of two different reconnection regimes, induced by a new topological association where null-point separatrices are embbeded in quasi-separatrix layers. This new topological association induces a change of field line connectivity, but also a continuous reconnection process, leading to an apparent slipping motion of reconnected field lines. From a MHD simulation of a such magnetic configuration association, involving open field lines, I showed that flare-accelerated particles can be injected in an extended coronal magnetic flux tube through a sweeping motion of energetic particle beams, injected succesively along slipping field lines.
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Contributor : Sophie Masson <>
Submitted on : Tuesday, January 4, 2011 - 4:17:40 AM
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  • HAL Id : tel-00551523, version 1


Sophie Masson. Les particules énergétiques solaires : études observationnelles et simulations magnétohydrdynamiques. Astrophysique [astro-ph]. Observatoire de Paris, 2010. Français. ⟨tel-00551523⟩



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