Annonce transmise par Nina Bizien (LPC2E)
Hi everyone,
I am pleased to invite you to my PhD defense, which will take place on Thursday 5th December in the Amphithéâtre Sadron at the LPC2E, Orléans. The defense will be in English. A zoom link is provided below.
Best wishes,
Nina
Title:
Evolution and Sources of Switchbacks Observed in the Solar Wind
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.
Composition of the jury:
ALEXANDROVA Olga, Rapportrice, Observatoire de Paris/LESIA
PATSOURAKOS Spiros, Rapporteur, Université d’Ioannina
LE CONTEL Olivier, Examinateur, LPP
VAN DRIEL-GESZTELYI Lidia, Examinatrice, MSSL — UCL, Konkoly Observatory
WILSON Lynn, Examinateur, NASA/GSFC
DUDOK DE WIT Thierry, Directeur de thèse, Université d’Orléans
FROMENT Clara, Co-encadrante, LPC2E, Orléans
Zoom link:
https://us02web.zoom.us/j/87830623594?pwd=bA1cfSbhDZnopWOjjQbf4cAOUjXTLy.1
Meeting ID: 878 3062 3594
Passcode: 291310