Multimodal rotating magnetoconvection in liquid metals

Turbulence and thermal convection, often strongly constrained by Lorentz and Coriolis forces, are ubiquitous in geophysical and astrophysical settings.

Rotating magnetoconvection (RMC), i.e. a fluid layer heated from below, cooled from above, rotating around the axis and permeated by an external vertical magnetic field, serves as an ideal theoretical testbed for elucidating the complex fluid dynamics of stellar and planetary interiors.

The RMC system is characterised by rich multimodal dynamics. Depending on the control parameters, the flow behaviour originates from a mix of boundary-attached, oscillatory, as well as geostrophic, magnetostrophic, and magnetic stationary modes. Specifically, convection in the form of thermal inertial oscillatory modes can only occur for Prandtl numbers Pr < 1, as characteristic for liquid metals and planetary cores. Theoretical predictions further indicate that these oscillatory modes compete with small-scale geostrophic and large-scale magnetostrophic modes in the geophysically most relevant regime in which planets reside.

Here, I will present results from direct numerical simulations of rotating magnetoconvection in liquid metals over a wide parameter space, concentrating on the impact of oscillatory convection. Albeit not very efficient in transporting heat, oscillatory convection is very efficient in transporting momentum and generating turbulence. Thus, it can fundamentally alter and even dominate the overall flow morphology, including the setting of the governing length scale. I will discuss the relevance of these results for our understanding of core convection and dynamo generation.