Numerical modelling of solar and stellar dynamos
Raphaël Raynaud (LRA)

Dynamo action, i.e. the self-amplification of a magnetic field by the flow of
an electrically conducting fluid, is considered to be the main mechanism for
the generation of the magnetic fields of stars and planets. Intensive and
systematic parameter studies by direct numerical simulations using the
Boussinesq approximation revealed fundamental properties of these models.
However, this approximation considers an incompressible conducting fluid, and
is therefore not adequate to describe convection in highly stratified systems
like stars or gas giants. A common approach to overcome this difficulty is then
to use the anelastic approximation, that allows for a reference density profile
while filtering out sound waves for a faster numerical integration. Through a
systematic parameter study of spherical anelastic dynamo models, we investigate
the influence of the stratification on the dynamo mechanisms, and compare them
with previous results obtained in the Boussinesq approximation. We discuss the
influence of the density stratification on the field geometry and the field
strength. Our results are in overall agreeement with the previous geodynamo
studies, and thus the main established results seem to be still relevant to the
study of stellar dynamos.