Flux emergence in a magnetized convection zone

Abstract

We study the influence of a dynamo magnetic field on the buoyant rise and emergence of twisted magnetic flux-ropes, and their influence on the global external magnetic field. We ran 3D MHD numerical simulations using the ASH code and analysed the dynamical evolution of such buoyant flux-ropes from the bottom of the convection zone until the post-emergence phases. The global nature of this model represents very crudely and inaccurately the local dynamics of the buoyant rise, but allows to study the influence of global effects such as self-consistently generated differential rotation, meridional circulation and Coriolis forces. Although motivated by the solar context, this model cannot be thought of as a realistic model of the rise of magnetic structures and their emergence in the Sun where the local dynamics are completely different. The properties of initial phases of the buoyant rise in good agreement with previous studies. However, the effects of the interaction of the background dynamo field become increase as the flux-ropes evolve. During the buoyant rise across the CZ, the flux-rope's magnetic field strength and scales as $rh{o}^a$, with $a\lesssim 1$. An increase of velocity, density and current precedes flux emergence at all longitudes. The geometry, latitude and relative orientation of the flux-ropes with respect to the background magnetic field influences the rise speeds, zonal flow amplitudes (which develop within the flux-ropes) and the corresponding surface signatures. This influences the morphology, duration and amplitude of the associated surface shearing and Poynting flux. The emerged flux influences the system's global polarity, leading in some cases to a polarity reversal while inhibiting background dynamo from doing so in some others. The emerged magnetic flux is slowly advected poleward, while being diffused and assimilated by the background dynamo field.

Accepted for publication in ApJ

References in corpus (14)

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Cited by in corpus (12)

• The Solar-Stellar Connection
• In Situ Properties of Small and Large Flux Ropes in the Solar Wind
• Thermal and non-thermal emission from reconnecting twisted coronal loops
• Theoretical limits on magnetic field strengths in low-mass stars
• Stirring the Base of the Solar Wind: On Heat Transfer and Vortex Formation
• Soft X-ray emission in kink-unstable coronal loops
• Multi-Parametric Study of Rising 3D Buoyant Flux Tubes in an Adiabatic Stratification Using AMR
• Magnetic flux concentrations from dynamo-generated fields
• Modeling the Rise of Fibril Magnetic Fields in Fully Convective Stars
• Interactions of twisted $\Omega$-loops in a model solar convection zone
• Successful and Failed Flux Tube Emergence in the Solar Interior
• 3D simulations of rising magnetic flux tubes in a compressible rotating interior: The effect of magnetic tension