Global magnetic cycles in rapidly rotating younger suns

TL;DR

This study uses advanced 3-D MHD simulations to explore how faster rotation in young sun-like stars influences magnetic dynamo action and cycle behavior, revealing magnetic wreaths with polarity reversals and buoyant magnetic loops.

Contribution

It demonstrates the impact of reduced diffusivity on magnetic wreath formation and cyclic behavior in stellar dynamos, advancing understanding of magnetic activity in young, rapidly rotating stars.

Findings

Magnetic wreaths exhibit prominent temporal variations and polarity reversals.

Lower diffusivity promotes the generation of cyclic magnetic structures.

Magnetic buoyancy can cause magnetic loops to rise toward the stellar surface.

Abstract

Observations of sun-like stars rotating faster than our current sun tend to exhibit increased magnetic activity as well as magnetic cycles spanning multiple years. Using global simulations in spherical shells to study the coupling of large-scale convection, rotation, and magnetism in a younger sun, we have probed effects of rotation on stellar dynamos and the nature of magnetic cycles. Major 3-D MHD simulations carried out at three times the current solar rotation rate reveal hydromagnetic dynamo action that yields wreaths of strong toroidal magnetic field at low latitudes, often with opposite polarity in the two hemispheres. Our recent simulations have explored behavior in systems with considerably lower diffusivities, achieved with sub-grid scale models including a dynamic Smagorinsky treatment of unresolved turbulence. The lower diffusion promotes the generation of magnetic wreaths that undergo prominent temporal variations in field strength, exhibiting global magnetic cycles that involve polarity reversals. In our least diffusive simulation, we find that magnetic buoyancy coupled with advection by convective giant cells can lead to the rise of coherent loops of magnetic field toward the top of the simulated domain.