MHD modelling at Newcastle University (dp263), DIaL2 and Cambridge HPC

Dynamics of stellar interiors

Figure 1 – streamlines of the magnetic field from the 3D dynamo simulations. The gold-blue magnetic field lines show a predominantly dipolar field geometry with the radiative envelope, whereas the green-purple magnetic field line reveal a more complex magnetic field topology inside the convective core.

Our group is currently studying magnetic massive stars (stars with convective cores and radiative envelopes), focusing on fluid wave generation and propagation in the radiation zones. We perform 2D/3D self-consistent simulations, where both the radiation zone and convection zone of a star are coupled in a cylindrical/spherical geometry, and include a magnetic field, either as an external forcing (2D), or through a self-developing stellar dynamo (3D). Our current aim is to investigate the effect of magnetism on the suppression of internal gravity waves in the radiation and how it affects observable signatures on stellar surfaces. 

Magnetic buoyancy and dynamo action in the solar tachocline

Figure 2 – A snapshot of the horizontal magnetic field from a magnetic buoyancy-driven dynamo simulation.

There is still no consensus regarding the dynamo mechanism that is responsible for generating the solar magnetic activity cycle. Whilst the potential role of differential rotation in the solar interior is well understood, additional physical processes must also contribute to any dynamo mechanism. In our numerical simulations, we have demonstrated that magnetic buoyancy in a shear-generated magnetic layer, in the presence of rotation, can drive a migratory (solar-like) dynamo. The DiRAC allocation has allowed us to significantly extend the time evolution of an early “proof of concept” simulation, to demonstrate that this system does indeed act as a dynamo. Resolution checks have also been carried out using our DiRAC time and these have highlighted some important features: due to nonlinear effects (with the initiation of the magnetic buoyancy instability depending crucially upon the strength of the magnetic layer, which evolves in time under the action of the imposed shear and magnetic diffusion), considerable care is needed when choosing suitable initial conditions in order to ensure that the dynamo does indeed operate successfully.