Large-scale 3D MHD simulation on the solar flux emergence and the small-scale dynamic features in an active region

TL;DR

This paper presents a 3D MHD simulation of solar flux emergence, revealing dynamic features like multiple magnetic separations and shearing motions that resemble observed active region behaviors.

Contribution

It introduces a novel 3D simulation demonstrating multiple magnetic separation events and their role in active region formation, aligning with observational phenomena.

Findings

Multiple magnetic separation events observed in the simulation.

Separated magnetic elements gather at active region edges.

Shearing motions of magnetic elements are consistent with observations.

Abstract

We have performed a three-dimensional magnetohydrodynamic simulation to study the emergence of a twisted magnetic flux tube from -20,000 km of the solar convection zone to the corona through the photosphere and the chromosphere. The middle part of the initial tube is endowed with a density deficit to instigate a buoyant emergence. As the tube approaches the surface, it extends horizontally and makes a flat magnetic structure due to the photosphere ahead of the tube. Further emergence to the corona breaks out via the interchange-mode instability of the photospheric fields, and eventually several magnetic domes build up above the surface. What is new in this three-dimensional experiment is, multiple separation events of the vertical magnetic elements are observed in the photospheric magnetogram, and they reflect the interchange instability. Separated elements are found to gather at the edges of the active region. These gathered elements then show shearing motions. These characteristics are highly reminiscent of active region observations. On the basis of the simulation results above, we propose a theoretical picture of the flux emergence and the formation of an active region that explains the observational features, such as multiple separations of faculae and the shearing motion.