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UID:119@atst.osups.universite-paris-saclay.fr
DTSTART;TZID=Europe/Paris:20251201T140000
DTEND;TZID=Europe/Paris:20251201T170000
DTSTAMP:20251124T221422Z
URL:https://atst.osups.universite-paris-saclay.fr/calendrier/these-etienne
 -berriot/
SUMMARY:Soutenance de thèse d'Étienne Berriot
DESCRIPTION:J'ai le plaisir de vous inviter à ma soutenance de thèse\, pr
 évue le lundi 1er décembre à 14:00 dans la salle du château sur le sit
 e de l'Observatoire à Meudon\, et intitulée “Solar wind radial evoluti
 on and dynamics of the heliospheric current sheet : Observations during a 
 Parker Solar Probe - Solar Orbiter radial alignment and hybrid simulations
  of magnetic reconnection”. Il y aura également une retransmission en 
 direct sur Youtube.\n\nDirecteurs de thèse: Olga Alexandrova et Pascal D
 émoulin (LIRA - Observatoire de Paris)\n\nMembres du Jury:\n\n 	Fabrice M
 ottez (LUX - Observatoire de Paris) - Président\n 	Marco Velli (Departmen
 t of Earth\, Planetary and Space Sciences - UCLA) - Rapporteur\n 	Benoit L
 avraud (Laboratoire d'Astrophysique de Bordeaux - Université de Bordeaux\
 , CNRS) - Rapporteur\n 	Miho Janvier (European Space Research and Technolo
 gy Centre - ESA) - Examinatrice\n 	Lorenzo Matteini (The Blackett Laborato
 ry\, Department of Physics - Imperial College London) - Examinateur\n 	Pet
 r Hellinger (Institute of Atmospheric Physics - Czech Academy of Sciences)
  - Invité\n 	Alexandra Alexandrova - Invitée\n\nAbstract:\n\nIn the sola
 r wind\, large-scale magnetic sectors of opposite polarities are separated
  by a thin layer called the heliospheric current sheet (HCS). The HCS\, as
  many other current sheets\, can undergo magnetic reconnection\, changing 
 the magnetic topoloy and abruptly converting magnetic energy towards heati
 ng\, particle acceleration\, and outflowing jets. Thus\, the magnetic reco
 nnection process strongly affects the dynamic and structuration of the HCS
 .\n\nThe goal of this thesis is the investigation of the solar wind radial
  evolution\, as well as magnetic reconnection dynamics in the context of a
  weakly collisional plasma.\n\nThe original approach is to study the same 
 plasma passing through two radially aligned spacecraft\, here Parker Solar
  Probe (PSP) and Solar Orbiter (SolO).  We developed a ballistic propagat
 ion method\, allowing the identification of the same density structure of 
 ~10^6 km radial extension passing through both spacecraft. This density st
 ructure was remarkably conserved during its ∼5.75 days of propagation be
 tween PSP at 0.1 au and SolO at 0.9 au. It is closely associated with the 
 HCS\, where reconnection jets are also detected at both radial distances.\
 n\nThe second main focus of this thesis is the study of a reconnecting cur
 rent sheet using hybrid-PIC numerical simulations with novel Möbius perio
 dic boundary conditions. Global dynamics of the tearing instability\, wher
 e several reconnection events are triggered along the same current sheet\,
  and its transition from the linear to non-linear stage are described.  D
 uring the non-linear stage\, a strong proton parallel temperature anisotro
 py\, with T_parallel &gt\; T_perp\, triggers the kinetic proton firehose i
 nstability. The energy conversion rates evolution in the whole domain and 
 around different regions of the unstable current sheet is quantified. In p
 articular\, these reveal that more heating is happening within the magneti
 c islands rather than around the X-points as is usually thought.\n\n(Trans
 mis par Étienne Berriot)
CATEGORIES:Séminaires et soutenances de thèse/HDR
LOCATION:Observatoire de Paris\, Meudon\, 2 place Jules Janssen\, Meudon\, 
 France
X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-ADDRESS=2 place Jules Janssen\, Meu
 don\, France;X-APPLE-RADIUS=100;X-TITLE=Observatoire de Paris\, Meudon:geo
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