Spontaneous Generation of delta-sunspots in Convective Magnetohydrodynamic Simulation of Magnetic Flux Emergence

TL;DR

This study models the spontaneous formation of delta-sunspots through flux emergence driven by turbulent convection, revealing natural processes that lead to complex active regions and potentially flare eruptions on the Sun.

Contribution

First simulation of delta-spot formation from flux emergence in a turbulent convection zone using advanced radiative MHD modeling.

Findings

Delta-spots form naturally from flux emergence and convection interactions.

Spot rotation and shear flows develop as a consequence of magnetic forces.

A flux rope structure is built up above the PIL, indicating potential flare activity.

Abstract

Observations reveal that strong solar flares and coronal mass ejections tend to occur in complex active regions characterized by delta-sunspots, spot rotation, sheared polarity inversion lines (PILs), and magnetic flux ropes. Here we report on the first modeling of spontaneous delta-spot generation as a result of flux emergence from the turbulent convection zone. Utilizing state-of-the-art radiative magnetohydrodynamics code R2D2, we simulate the emergence of a force-free flux tube in the convection zone that stretches down to -140 Mm. Elevated by large-scale convective upflows, the tube appears on the photosphere as two emerging bipoles. The opposite polarities collide against each other due to the subsurface connectivity, and they develop into a pair of closely-packed delta-spots. The Lorentz force drives the spot rotation and a strong counter-streaming flow of 10 km/s at the PIL in delta-spots, which, in tandem with local convection, strengthens the horizontal field to 4 kG and builds up a highly-sheared PIL. In the atmosphere above the PIL, a flux rope structure is created. All these processes follow the multi-buoyant segment theory of the delta-spot formation, and they occur as a natural consequence of interaction between magnetic flux and turbulent convection, suggesting that the generation of delta-spots and the resultant flare eruptions may be a stochastically determined process.