Soutenance de thèse de Manon Jarry le 13/09/24

Annonce transmise par Manon Jarry (IRAP)

Hi everyone,

I am pleased to invite you to my PhD defense, which will take place on Friday 13 September 2024 at 2pm in the Coriolis room at the IRAP, OMP (14 avenue Edouard Belin, 31400 Toulouse). The defense will be in English.

Title :

« Role of coronal shock waves and flares in the acceleration of solar energetic particles »

Abstract :


Coronal and interplanetary shock waves are produced by fast and wide coronal mass ejections (CMEs). They are major drivers of space-weather phenomena as they can directly perturb the near-Earth environment and induce significant changes in heliospheric particle radiation levels. These shock fronts are thought to accelerate solar particles to high energies through diffusive-shock acceleration. Another known efficient solar particle accelerator is the solar flare, another by-product of a forming CME through magnetic reconnection. Since shock waves and flares occur concomitantly, it is difficult to distinguish the relative contributions of the two accelerators. In order to contribute to improve our understanding of these acceleration processes, this thesis investigates the intricate relationship between these CME-driven shock waves, their associated X-ray flares, and their resulting solar energetic particles (SEPs) events. Advanced observational and modelling techniques are required to isolate the effects of each source. Over the last decades, instruments on STEREOs, SOHO, SDO, and more recently PSP and Solar Orbiter spacecrafts provide in-situ measurements and remote-sensing observations of these complex events. The evolution of CME-driven shock waves from the corona into the interplanetary medium can be modelled with 3D ellipsoids derived from multi-viewpoint imagery. A parametric study was carried out on 33 strong pressure waves observed between 2011 and 2017 and reconstructed using this technique. A classical expansion and propagation profile for a shock wave in the corona has been established, revealing a spherical expansion until that the propagation speed became constant. A correction factor has also been proposed to take account of the projection effect in the speed estimates from a single point of view. A study of the soft and hard X-ray (SXR and HXR) fluxes of flares associated with these shocks confirmed the well-known Neupert effect and the strong correlation between the maximum of these fluxes. The shock wave speed is temporally correlated with the SXR flux and the shock wave acceleration with the HXR flux. An already established correlation between the radial velocity of the shock wave and the maximum SXR flare is updated with our sample of strong events. In this one, all X-class flares are associated with CMEs reaching speeds of at least 1000 km/s. The magneto-hydrodynamic (MHD) properties of the expanding shock and the magnetic field lines in the corona can be derived using MHD cubes. As the shock evolves, its geometry and kinematics change rapidly along the magnetic field lines connected to the spacecraft that record the SEPs. Through the study of a particular event, we found temporal correlations between the early evolution of shock wave parameters and the associated SEP event properties. A strong temporal agreement is found between the formation of the modelled shock wave and the estimated release times for both electrons and protons, suggesting a common acceleration process. The elevated electron-to-proton ratio during the early SEP event phase coincide with the highly quasi-perpendicular phase of the shock, suggesting that its rapid evolution as it transits from the low to the high corona modifies the conditions under which particles are accelerated. The combined study of abundance ratios such as Fe/C with the early evolution of the shock geometry reveals that, contrary to the results of previous studies, a high Fe/C at high energy is not systematically linked to a quasi-perpendicular shock geometry. On the other hand, the observations suggest that pre-event solar activity plays a significant role in modifying the local coronal composition, thus affecting SEPs composition independent of shock acceleration efficiency. Using particle transport codes in which we integrate these shocks, comparisons between observations and simulations are made to identify the key shock parameters in the acceleration process.

Composition of the jury :

Referees :
Nicole Vilmer, LESIA - Observatoire de Paris - PSL/CNRS/Sorbonne Universités/Université Paris Diderot

Miho Janvier, ESTEC - European Space Agency

Examinators :

Alexander Warmuth, Leibniz-Institut für Astrophysik Potsdam (AIP)

Rami Vainio, University of Turku
Pierre-Louis Blelly, IRAP

Supervisors :

Alexis Rouillard, IRAP
Illya Plotnikov, IRAP

Zoom link :

It will be possible to attend by videoconference via this link :
https://cnrs.zoom.us/j/92359077048?pwd=ITy6aIk7pEtyuOgvCcn31BN49XqUwP.1

Meeting ID: 923 5907 7048
Secret code: IRAP123

Celebration :

You are also invited to join us for a drink after the defense in the OMP cafeteria.

Best regards,

Manon Jarry