A5034258185- Solar and Space Plasma Dynamics
- Geomagnetism and Paleomagnetism Studies
- Astro and Planetary Science
- Stellar, planetary, and galactic studies
- Geophysics and Gravity Measurements
- Astrophysics and Star Formation Studies
- Ionosphere and magnetosphere dynamics
- Solar Radiation and Photovoltaics
- History and Developments in Astronomy
- Photocathodes and Microchannel Plates
- Global Energy and Sustainability Research
- Solar Energy Systems and Technologies
- Atmospheric Ozone and Climate
- Hydrocarbon exploration and reservoir analysis
- Economic and Technological Developments in Russia
- Space Science and Extraterrestrial Life
- Spacecraft and Cryogenic Technologies
- Methane Hydrates and Related Phenomena
- Astronomy and Astrophysical Research
- Geophysical and Geoelectrical Methods
Centre National de la Recherche Scientifique
2014-2024
Université de Toulouse
2014-2024
Université Toulouse III - Paul Sabatier
2012-2024
Institut de Recherche en Astrophysique et Planétologie
2012-2023
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2007-2019
Astrophysique, Instrumentation et Modélisation
2007-2019
CEA Paris-Saclay
2015-2019
Institut für Sonnenphysik
2017
Université Paris Cité
2007-2017
Institut de Recherche sur les Lois Fondamentales de l'Univers
2012-2017
Context.The Sun is a magnetic star whose magnetism and cyclic activity linked to the existence of an internal dynamo.
Context. The solar magnetic activity and cycle are linked to an internal dynamo. Numerical simulations efficient accurate tool investigate such intricate dynamical processes.
We present the first 3D MHD study in spherical geometry of non-linear dynamical evolution magnetic flux tubes a turbulent rotating convection zone. numerically rise toroidal ropes from base modelled zone up to top our computational domain where bipolar patches are formed. compare behaviour fully convective shell possessing self-consistently generated mean flows such as meridional circulation and differential rotation, with reference calculations done quiet isentropic find that two parameters...
Aims: To understand stellar magnetism and to test the validity of Babcock-Leighton flux transport mean field dynamo models with activity observations Methods: 2-D at various rotation rates are computed STELEM code study sensitivity cycle period butterfly diagram parameter changes compared observational data. The novelty is that these incorporate scaling laws deduced from 3-D hydrodynamical simulations for influence rate on amplitude profile meridional circulation. These make also use...
We study the connections between Sun's convection zone and evolution of solar wind corona. let magnetic fields generated by a 2.5-dimensional (2.5D) axisymmetric kinematic dynamo code (STELEM) evolve in 2.5D coronal isothermal magnetohydrodynamic (DIP). The computations cover an 11 year activity cycle. wind's asymptotic velocity varies latitude time good agreement with available observations. polarity reversal happens at different paces heights. Overall mass-loss rate, momentum flux, braking...
We aim at a highly sensitive search for weak magnetic fields in main sequence stars of intermediate mass, by scanning classes with no previously reported members. After detecting field on the normal, rapidly rotating A-type star Vega, we concentrate here bright Sirius A, taken as prototypical, chemically peculiar, moderately Am star. employed NARVAL and ESPaDOnS high-resolution spectropolarimeters to collect 442 circularly polarized spectra, complemented 60 linearly spectra. Using list about...
Context. An extremely weak circularly polarized signature was recently discovered in spectral lines of the chemically peculiar Am star Sirius A. A surface magnetic field proposed to account for observed signal, but shape phase-averaged signature, dominated by a prominent positive lobe, is not expected standard theory Zeeman effect.
Abstract The emergence of active regions on the Sun is an integral feature solar dynamo mechanism. However, details about generation active-region-scale magnetism and journey this magnetic flux from interior to photosphere are still in question. Shifting paradigms now developing for source depth Sun’s large-scale magnetism, organization into fibril tubes, role convection shaping active-region observables. Here we review landscape theories simulations, highlight plays global process, make...
We present three-dimensional numerical simulations of a magnetic loop evolving in either convectively stable or unstable rotating shell. The is introduced the shell such way that it buoyant only certain portion longitude, thus creating an \Omega-loop. Due to action buoyancy, rises and develops asymmetries between its leading following legs, emerging bipolar regions whose characteristics are similar ones observed spots at solar surface. In particular, we self-consistently reproduce creation...
In a uniformly rotating fluid, inertial waves propagate along rays that are inclined to the rotation axis by an angle depends on wave frequency. closed domains, multiple reflections from boundaries may cause focus particular structures known as attractors. Such have previously been studied theoretical point of view, in laboratory experiments, linear numerical calculations and some recent simulations. present paper, two-dimensional direct simulations attractor presented. regime, we first...
The question of the origin and evolution magnetic fields in stars possessing a radiative envelope, like A-type stars, is still regarded as challenge for stellar physics. Those zones are likely to be differentially rotating, which suggests that strong interactions between differential rotation could at play. We numerically compute joint velocity 3D spherical shell starting from an initial profile poloidal field rotation. initially wound-up by produce toroidal becomes unstable. In particular...
We consider a conventional α-Ω-dynamo model with meridional circulation that exhibits typical features of the solar dynamo, including Hale-cycle period around 20 years and reasonable shape butterfly diagram. With regard to recent ideas tidal synchronization cycle, we complement this by an additional time-periodic α-term is localized in tachocline region. It shown amplitudes some decimeters per second are sufficient for become capable entraining underlying dynamo. argue such α may indeed be...
We report the analysis, conducted as part of MaTYSSE programme, a spectropolarimetric monitoring ~0.8 Myr, ~1.4 MSun disc-less weak-line T Tauri star V410 Tau with ESPaDOnS instrument at Canada-France-Hawaii Telescope and NARVAL T\'elescope Bernard Lyot, between 2008 2016. With Zeeman-Doppler Imaging, we reconstruct surface brightness magnetic field Tau, show that is heavily spotted possesses ~550 G relatively toroidal field. find features weak level differential rotation equator pole ~5...
Magnetohydrodynamic interactions between plasma flows and magnetic fields is fundamental to the origin sustenance of 11-year sunspot cycle. These processes are intrinsically three-dimensional (3D) in nature. Our goal construct a 3D solar dynamo model that on one hand captures buoyant emergence tilted bipolar pairs, other produces cyclic large-scale field reversals mediated via surface flux-transport -- is, Babcock-Leighton mechanism. We perform kinematic simulations where prescribed velocity...
We have developed a variational data assimilation technique for the Sun using toy αΩ dynamo model. The purpose of this work is to apply modern techniques solar physically based This represents first step toward complete model magnetism. derive adjoint code and use minimization procedure invert spatial dependence key physical ingredients find that very powerful leads encouraging results will be applied more realistic dynamo.
This article reviews the current knowledge and status of investigations on variable magnetic activity cool stars. We discuss Sun in context solar‐type stars, highlighting peculiarities common features terms its variability over different time scales. examine how both theory observations are providing new clues about main physical processes that generate fields interior as well those lead to evolving stellar surface magnetism varying chromospheric coronal phenomena. then proceed relations...
The Sun is a magnetic star whose cyclic activity thought to be linked internal dynamo mechanisms. A combination of numerical modelling with various levels complexity an efficient and accurate tool investigate such intricate dynamical processes. We the role buoyancy process in 2D Babcock-Leighton models, by more accurately surface source term for poloidal field. Methods. To do so, we reintroduce mean-field models results full 3D MHD calculations non-linear evolution rising flux tube...
Context. The transport of angular momentum and chemical elements within evolving stars remains poorly understood. Asteroseismic spectroscopic observations low-mass main sequence red giants reveal that their radiative cores rotate orders magnitude slower than classical predictions from stellar evolution models the abundances surface light are too small. Magnetohydrodynamic (MHD) turbulence is considered a primary mechanism to enhance in interiors but its efficiency still largely uncertain....
ABSTRACT Observations of surface magnetic fields cool stars reveal a large diversity configurations. Although there is now consensus that these are generated through dynamo processes occurring within the convective zone, physical mechanism driving such variety field topologies still debated. This paper discusses possible origins dipole- and multipole-dominated morphologies using three-dimensional numerical simulations stratified systems where feedback on fluid motion significant. Our main...
The present study aims at studying the flow and field produced by a stellar radiative zone which is initially made to rotate differentially in presence of large-scale poloidal magnetic threading whole domain. We focus both on axisymmetric configurations initial winding-up lines possible instabilities those configurations. aim particular assessing role stratification stabilising system. perform 2D 3D global Boussinesq numerical simulations started from an radial or cylindrical differential...
Whitepaper #287 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional research/applications/operations pipeline; solar physics; space-based missions/projects; […]
We present in this work the development of a solar data assimilation method based on an axisymmetric mean field dynamo model and magnetic surface data. Our midterm goal is to predict quasi-cyclic activity. Here we focus ability our algorithm constrain deep meridional circulation Sun observations. To that end, develop variational technique. Within given window, procedure minimizes differences between forecast from by finding optimal convection zone initial via quasi-Newton algorithm....
Abstract This study aims at investigating the ability of strong interactions between magnetic field concentrations during their rise through convection zone to produce complex active regions solar surface. To do so, we perform numerical simulations buoyant structures evolving and interacting in a model zone. We first 3D rotating then introduce idealized close bottom computational domain. These possess certain degree line twist they are made on particular extension longitude. The resulting...
We present recent 3-D MHD numerical simulations of the non-linear dynamical evolution magnetic flux tubes in an adiabatically stratified convection zone spherical geometry, using anelastic harmonic (ASH) code. seek to understand mechanism emergence strong toroidal fields from base solar surface as active regions. confirm results obtained cartesian geometry that are not twisted split into two counter vortices before reaching top zone. Moreover, we find undergo poleward-slip instability due...
Recent spectropolarimetric surveys of main-sequence intermediate-mass stars have exhibited a dichotomy in the distribution observed magnetic field between kG dipoles Ap/Bp and sub-Gauss magnetism Vega Sirius. We would like to test whether this is linked stability versus instability large-scale configurations differentially rotating radiative zones. computed axisymmetric obtained from evolution dipolar threading shell. A full parameter study including various density profiles initial boundary...