Description du sujet de thèse

Study of thermal non-equilibrium in the solar atmosphere and its possible effects on the solar wind dynamics

Contexte de travail

The Sun's outer atmosphere, the solar corona, is a hot and tenuous environment whose dynamics are controlled by the evolution of the solar magnetic field. Closed and open field structures coexist in the solar atmosphere, respectively confining the plasma and forming coronal loops, or allowing it to escape freely into the interplanetary medium and, as such, feeding the solar wind.
This PhD project will be part of the ANR (Agence National de la Recherche) “CROSSWIND - What is the imprint of the multi-scale variability of solar closed-field structures in the Solar Wind? » project.
The goal of this projet is to study the interplay between the thermodynamics of the plasma and magnetic reconnection in the solar corona. More specifically, we will study the mechanisms of thermal non-equilibrium (TNE) and interchange reconnection (ICR) – magnetic reconnection at boundaries between closed and open field structures. TNE is a thermodynamical state set by stratified (mainly at the footpoints) and quasi-steady heating. TNE is observed in the majority of coronal loops in active regions and manifests as chromospheric evaporation and coronal condensation (coronal rain) cycles. As such TNE is a key process for the mass and energy transport in the solar atmosphere [1]. Up to now the consequences of this mechanism for the solar wind are unknown.
The goal of this project it to test the hypothesis that TNE is also present at the closed-field sources of the solar wind, at open-closed boundaries. For example, TNE could constrain the ICR process by driving cyclic ICR in pseudo-streamers, at fine-spine topologies (FSTs) and at the edge of active regions (AR) in the so-called « fan loops ». It could also inject mass and energy into the solar wind by its interplay with ICR. Our two main objectives are: (1) to characterize TNE cycle events at the sources of the solar wind and (2) to estimate the solar wind variability driven by TNE cycles.
The PhD student will directly contribute to the project by :
- Analysing magnetohydrodynamic (MHD) simulations (with the MAS [2] and ARMS [3] codes) of a solar active regions, FSTs and pseudo-streamers. They will be able to start from existing simulation runs and will participate the the elaboration of new ones.
- Comparing their results with observations from space missions such as SDO, Solar Orbiter, Hinode, IRIS etc
- Investigating the potential link between the dynamics at the solar sources and the solar wind variability observed in situ (Parker Solar Probe, Solar Orbiter) and with heliospheric imagers (onboard Parker Solar Probe, Solar Orbiter, Proba-3, PUNCH etc)
Prerequisites:
- Master in physics
- a solid grounding in astrophysics and/or plasma physics is a plus,
- Python and IDL programming basic. Advanced level is a plus,
- ability to work in a team,
- autonomy, initiative and scientific curiosity.
References:
1. P. Antolin and C. Froment. “Multi-Scale Variability of Coronal Loops Set by Thermal Non-Equilibrium and Instability as a Probe for Coronal Heating”. In: Frontiers in Astronomy and Space Sciences 9 (2022).
2. Z. Mikić et al. “Predicting the corona for the 21 August 2017 total solar eclipse”. In: Nature Astronomy 2.11 (2018).
3. T. Pellegrin-Frachon et al. “ICR dynamics in a solar coronal pseudo-streamer”. In: A&A 675 (2023).

Contraintes et risques

The Laboratoire de Physique et de Chimie de l'Environnement et de l'Espace (LPC2E), a space laboratory located on the CNRS campus in Orléans, is affiliated with the CNRS, the University of Orléans and the CNES. It comprises three scientific teams, one of which focuses on solar-terrestrial relations and space plasmas. The laboratory has strong expertise in space instrumentation, from design to production and implementation of on-board instruments on satellites. We develop instruments that have flown or are flying on several space missions such as Solar Orbiter, BepiColombo, and Parker Solar Probe.
The LPC2E is located on the outskirts of Orléans, a medium-sized city on the banks of the Loire, an hour's train ride south of Paris. Living conditions are considerably less expensive in Orléans than in Paris. The CNRS campus in Orléans offers an exceptional research environment with state-of-the-art facilities. The working languages in our team are English and French as we come from different countries.
The PhD student will join the space plasma physics team at team and more specifically the team the CROSSWIND project that is composed of one researcher and a postdoc and international collaborators from Predictive Science Inc. in San Diego, USA, the University of Oslo, Norway, LPP in Paris and IRAP in Toulouse.

The aim of the thesis is to provide the PhD student with a comprehensive training program, including practical aspects such as data processing, the development of multi-instrument analysis skills, and a solid understanding of the physical processes that play a key role in the solar atmosphere.