Self-assembly of shallow magnetic spots through strongly stratified turbulence

Abstract

Recent studies have demonstrated that in fully developed turbulence, the effective magnetic pressure of a large-scale field (non-turbulent plus turbulent contributions) can become negative. In the presence of strongly stratified turbulence, this was shown to lead to a large-scale instability that produces spontaneous magnetic flux concentrations. Furthermore, using a horizontal magnetic field, elongated flux concentrations with a strength of a few per cent of the equipartition value were found. Here we show that a uniform vertical magnetic field leads to circular magnetic spots of equipartition field strengths. This could represent a minimalistic model of sunspot formation and highlights the importance of two critical ingredients: turbulence and strong stratification. Radiation, ionization, and supergranulation may be important for realistic simulations, but are not critical at the level of a minimalistic model of magnetic spot formation.

6 pages, 5 figures, revised version, ApJL (in press)

References in corpus (4)

• The case for a distributed solar dynamo shaped by near-surface shear
• Magnetic Cycles in a Convective Dynamo Simulation of a Young Solar-type Star
• Large-scale dynamos in turbulent convection with shear
• On the Formation of Active Regions

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