Missions

The temperature of the solar atmosphere increases from thousands to millions of degrees from the lower layer, the chromosphere, to the outermost one, the corona, while density drops accordingly. Such a phenomenon is called temperature inversion and how it happens is still largely unknown. Recently, a new kinetic model of coronal loop has been introduced, describing a collisionless plasma confined in a semicircular tube subjected to the Sun's gravity, in thermal contact with a collisional chromosphere behaving as a thermostat at the loop's feet. This kinetic model has shown that rapid, intermittent and short-lived heating events in the chromosphere can drive the coronal plasma towards a stationary state with suprathermal tails in the particles' velocity distribution functions, exhibiting temperature and density profiles strikingly similar to those observed in the atmosphere of the Sun. These results suggest that a million-Kelvin solar corona can be produced without the local deposition in the upper layer of the atmosphere typically assumed by standard approaches.
The mission of this offer is to build on these recent advances, and to develop the newly developed kinetic model in order that it can include collisions and therefore account for irreversible effects like heat conduction. Such effects – which have not yet been investigated in the frame of this approach – will change the energy balance in the corona and the temperature profile as a consequence. Investigating how this change occur is of a strong interest, both for fundamental reasons and for applications to the physics of the solar and stellar atmospheres.

Activities

Along the 2 years duration contract, the activities will consist in:
- Developing a collisionless kinetic model for the solar corona, including an electric field fully decomposed in N much larger than 1 Fourier modes (contrary to the basic model which include only N=1 mode)

- Studying the role of collisionality for temperature inversion in the corona. This can be investigated by following two main strategies: 1/ a fully numeric strategy, using numerical codes taking into account Coulomb interactions (like the BiCop code developed by our colleague Pr. Simone Landi from university of Florence, Italy). And 2/ a semi-analytical approach, based on the addition to the collisionless model of a diffusion term, and the subsequent treatment of the particle's dynamics according to stochastic (Langevin) differential equations.

Skills

The candidate will need a solid background in statistical and kinetic physics, as well as plasma and solar physics. An experience in numerical simulation and computational physics are also required.

Work Context

The candidate will work in the HPA group of the Laboratoire d'Etudes et d'Instrumentation en Astrophysique (LESIA) of the Paris Observatory in Meudon. Here he will work with Arnaud Zaslavsky and with other researchers from the group, which specializes in Solar and Plasma physics. The candidate will benefit from all the facilities available at Meudon for scientific purposes (computational center) and non-scientific (cantine, access to CLAS center for activities…)

Constraints and risks

Nothing specific is identified with this respect.