Emergence of a partially split flux tube into the solar atmosphere

We performed a three-dimensional MHD simulation for the emergence of a partially split flux tube into the solar atmosphere, which was focused on the mechanism of activity observed on the Sun, such as the merging of magnetic polarity regions in the photosphere and the formation of multi-flux domains in the corona. The simulation reproduced that a small polarity region associated with a rotational flow merges into a main polarity region, and the main polarity region later develops a rotational flow in the same direction as the small polarity region. In accordance with the photospheric merging process, multi-flux domains form in the corona and a current layer separating these flux domains travels outward as the flux domains expand. We also investigated the time variations of the magnetic flux, energy, and helicity injected into the atmosphere by the partially split flux tube to see the nature of helicity injection in a multi-pole system.