On December 5, 2024, Nina Bizien brilliantly defended her thesis entitled “Evolution and Sources of Switchbacks Observed in the Solar Wind”. Well done Nina!
Abstract:
Recent observations by the Parker Solar Probe (PSP) mission, launched in 2018, provide new clues on the origin of the solar wind. The scientific goal of the mission is to reveal the physical mechanisms closest to the Sun that are linked to two fundamental and unresolved questions, the problem of heating and acceleration of the solar wind. The mission revealed the ubiquity of sudden deflections of the solar wind’s magnetic field, known as switchbacks. These structures, which propagate at the Alfvén speed, could be the source of energy transfers that answer these questions. Their origin and their ability to survive in the solar wind have yet to be elucidated.
The work carried out in this thesis aims to understand the origin and evolution of switchbacks based on both in situ magnetic field measurements and remote sensing observations. First, I focus on the nature of switchback boundaries, the intervals that include most of the magnetic field deflection. Due to the complex 3D structure of these boundaries, their analysis requires the definition of a new methodology. I show that the nature of the boundaries corresponds to closed structures, which is a new result. This has an implication on the propagation of switchbacks, as the results suggest that their erosion may be much slower than expected. This, in turn, may explain why we observe switchbacks far from the Sun. The results are also compatible with an origin of switchbacks that is rooted in the lower solar atmosphere, which motivates the second part of my thesis. There are various non-exclusive hypotheses as to the origin of switchbacks, including an origin in the Sun’s lower atmosphere. Nevertheless, there is currently a consensus on the role that small reconnection events play in the Sun’s lower corona in creating conditions for generating switchbacks through magnetic reconnection. This hypothesis has yet to be verified due to the difficulty of relating transient events in the corona with structures propagating in the solar wind. The aim of this study is to establish, statistically and through observations, whether jets from coronal bright points located in coronal holes can be precursors of switchbacks. Although this study is the most detailed approach to date, the results show no clear correlation. Different reasons are considered. The implemented models would not be precise enough to study the small-scale eruptive events, that would require a finer analysis of the magnetic topology in the lower corona. Evolutionary changes during solar wind propagation could affect our findings. It could also mean that a wider range of eruptive events, not just jets, might be the precursors of switchbacks.
Keywords: Solar Wind, Solar Corona, Parker Solar Probe, Switchbacks
Jury members:
ALEXANDROVA Olga, Reviewer, Observatoire de Paris/LESIA
PATSOURAKOS Spiros, Reviewer, Université d’Ioannina
LE CONTEL Olivier, Examiner, LPP
VAN DRIEL-GESZTELYI Lidia, Examiner, MSSL — UCL, Konkoly Observatory
WILSON Lynn, Examiner, NASA/GSFC
DUDOK DE WIT Thierry, Thesis Supervisor Université d’Orléans
FROMENT Clara, Thesis Co-Supervisor, LPC2E, Orléans