Modelling magnetic flux emergence in the solar convection zone

Abstract

[Abridged] Bipolar magnetic regions are formed when loops of magnetic flux emerge at the solar photosphere. Our aim is to investigate the flux emergence process in a simulation of granular convection. In particular we aim to determine the circumstances under which magnetic buoyancy enhances the flux emergence rate (which is otherwise driven solely by the convective upflows). We use three-dimensional numerical simulations, solving the equations of compressible magnetohydrodynamics in a horizontally-periodic Cartesian domain. A horizontal magnetic flux tube is inserted into fully developed hydrodynamic convection. We systematically vary the initial field strength, the tube thickness, the initial entropy distribution along the tube axis and the magnetic Reynolds number. Focusing upon the low magnetic Prandtl number regime (Pm<1) at moderate magnetic Reynolds number, we find that the flux tube is always susceptible to convective disruption to some extent. However, stronger flux tubes tend to maintain their structure more effectively than weaker ones. Magnetic buoyancy does enhance the flux emergence rates in the strongest initial field cases, and this enhancement becomes more pronounced when we increase the width of the flux tube. This is also the case at higher magnetic Reynolds numbers, although the flux emergence rates are generally lower in these less dissipative simulations because the convective disruption of the flux tube is much more effective in these cases. These simulations seem to be relatively insensitive to the precise choice of initial conditions: for a given flow, the evolution of the flux tube is determined primarily by the initial magnetic field distribution and the magnetic Reynolds number.

arXiv comment12 pages, 15 figures, 2 tables. Accepted for publication in Astronomy and Astrophysics

References in corpus (6)

• Simulation of the Formation of a Solar Active Region
• Magnetic flux emergence in granular convection: Radiative MHD simulations and observational signatures
• Twisted flux tube emergence from the convection zone to the corona
• Solar Flux Emergence Simulations
• Convective intensification of magnetic fields in the quiet Sun
• Flux-loss of buoyant ropes interacting with convective flows

Cited by in corpus (3)

• Photospheric Velocity Structures during the Emergence of Small Active Regions on the Sun
• Coronal heating problem solution by means of axion origin photons
• Thermomagnetic Ettingshausen-Nernst effect in tachocline, magnetic reconnection phenomenon in lower layers, axion mechanism of solar luminosity variations, coronal heating problem solution and mechanism of ADM variations around BH