Subsurface magnetic field and flow structure of simulated sunspots

TL;DR

This study uses numerical models to analyze the subsurface magnetic and flow structures of sunspots, revealing how deep flows and magnetic flux separation influence sunspot evolution and surface appearance.

Contribution

It provides new insights into the subsurface flow and magnetic field configurations of sunspots using deep domain simulations, reducing boundary condition effects.

Findings

Magnetic flux is pushed into downflow vertices beneath sunspots.

Large-scale radial outflows develop around sunspots within a day.

Deep domains lessen boundary condition impacts on sunspot stability.

Abstract

We present a series of numerical sunspot models addressing the subsurface field and flow structure in up to 16 Mm deep domains covering up to 2 days of temporal evolution. Changes in the photospheric appearance of the sunspots are driven by subsurface flows in several Mm depth. Most of magnetic field is pushed into a downflow vertex of the subsurface convection pattern, while some fraction of the flux separates from the main trunk of the spot. Flux separation in deeper layers is accompanied in the photosphere with light bridge formation in the early stages and formation of pores separating from the spot at later stages. Over a time scale of less than a day we see the development of a large scale flow pattern surrounding the sunspots, which is dominated by a radial outflow reaching about 50% of the convective rms velocity in amplitude. Several components of the large scale flow are found to be independent from the presence of a penumbra and the associated Evershed flow. While the simulated sunspots lead to blockage of heat flux in the near surface layers, we do not see compelling evidence for a brightness enhancement in their periphery. We further demonstrate that the influence of the bottom boundary condition on the stability and long-term evolution of the sunspot is significantly reduced in a 16 Mm deep domain compared to the shallower domains considered previously.