Soutenance de thèse de Chen Xing (LPP) le 27 nov 2023 à 08h00

Title: The Role of Magnetic Reconnection in the Evolution of Solar Eruptive Flux Ropes.

Date: 27 November 2023, 08:00 (CET)

Location: Room 402, School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing, China.

Online meeting link: https://cnrs.zoom.us/j/96919917416?pwd=MDZZMXplM1hJVUU1RC9KS1BHOU84Zz09
Meeting ID: 969 1991 7416
Secret code: 4jfn3P

Language: English

Jury:

Jingxiu WANG, Professor, National Astronomical Observatories, Chinese Academy of Sciences (President, Referee)
Karine BOCCHIALINI, Professor, Universite Paris-Saclay - Institut d’Astrophysique Spatiale (Referee)
Chaowei JIANG, Professor, Institute of Space Science and Applied Technology, Harbin Institute of Technology, Shenzhen (Referee)
Patrick HENNEBELLE, Director of research, Commissariat à l’énergie atomique et aux énergies alternatives - Astrophysique Instrumentation Modélisation (Examiner)
Pengfei CHEN, Professor, School of Astronomy and Space Science, Nanjing University (Examiner)
Guillaume AULANIER, Astronomer, Observatoire de Paris - Laboratoire de Physique des Plasmas (Supervisor)
Xin CHENG, Professor, School of Astronomy and Space Science, Nanjing University (Co-supervisor)
Mingde DING, Professor, School of Astronomy and Space Science, Nanjing University (Co-supervisor)

Abstract:

Coronal mass ejections (CMEs) are impulsive eruptions of plasmas in the solar corona. Their interaction with the Earth's magnetosphere can induce extreme space weather conditions, with a major impact on human activities related to advanced technologies. A thorough understanding of the evolution of CMEs and their progenitors is extremely important for predicting CME eruptions and their related space weather. In this thesis, using numerical simulations and space observations, we study the kinematics, thermal properties and magnetic field evolution of flux ropes in CME progenitors and CMEs, and especially, the specific role of magnetic reconnection. We have discovered that the initiation of CMEs before their impulsive rise is a multiple-physics coupled-process. We have shown that the initiation of CMEs is first triggered and driven by the reconnection in hyperbolic flux tubes, and then driven by the coupling of torus instability and reconnection. We have also shown that the hot channel before the impulsive ejection is built up by hot flux rope field lines, the latter of which are progressively formed and heated by slipping reconnection in thin current sheets surrounding the flux rope. We also studied the evolution of magnetic flux in CMEs, and found that the pre-eruptive flux rope, rather than the magnetic reconnection during the eruption, is most likely the main contributor to the toroidal flux of the CME. More specifically, the magnetic reconnection first increases and then decreases the toroidal flux of the CME flux rope during the eruption. In addition, we studied two new observational phenomena related to CMEs and flares in the solar lower atmosphere, which are manifestations of the growth and deformation of flux ropes in CME progenitors and CMEs induced by magnetic reconnection. Finally, we have proposed two methods for identifying the footpoints of flux ropes associated with CMEs, which will be very useful for future work aimed at studying their evolution in the solar corona and interplanetary space.