La fédération
Intranet
Séminaire IPAG
ISTerre seminar: The interplay between tidal flows and magnetic fields in stellar or planetary convective envelopes
jeudi 16 janvier 2025 - 11h00
Aurélie Astoul - U. of Leeds---
Tidal interactions are a key driver of orbital and rotational evolution in compact stellar and (exo-)planetary systems. In the convective envelopes of solar-like stars and giant gaseous planets, the tidal response takes the form of tidal flows, including (magneto-)inertial waves which are expected to be highly dissipative when they are excited. Convective envelopes are usually magnetised due to the dynamo effect, but the interactions between magnetic fields and tidal waves have not been well explored yet. In this vein, I will present exploratory nonlinear MHD simulations of tidally-excited waves in spherical convective shells. In our model, wavelike tides are forced by an effective body force in an incompressible rotating fluid (as a first approach), harbouring an initially dipolar magnetic field. Simulations with weak magnetic fields exhibit tidally-generated differential rotation in the form of zonal flows as in the hydrodynamical case. This cylindrical-like differential rotation can substantially modify tidal dissipation rates from prior linear predictions. This is particularly true for thin shells, high tidal amplitudes, and low viscosities, for which non-linear effects (including wave-wave and wave-zonal flow interactions) are strong. Moreover, (non-)axisymmetric tidal flows affect the amplitude and structure of the magnetic field, notably through creation of toroidal fields via the omega effect. We also observe a strong quadrupolar poloidal magnetic response due to the type of forcing used. In contrast, simulations with strong magnetic fields feature inhibited zonal flows due to large-scale magnetic torques, possibly involving torsional waves at the transition between the two regimes for intermediate magnetic fields. For high magnetic Prandtl number, evidences of magnetic instabilities are observed, and I will discuss the possibility of magneto-rotational instabilities. This seminar proposed by ISTerre will take place in Dolomieu Room, in Maison des Géosciences, 1381 rue de la piscine, Campus de St Martin d'Hères.