Three-dimensional magnetohydrodynamic simulation of the solar magnetic flux emergence

Context. Solar active regions are formed through the emergence of magnetic flux from the deeper convection zone. Recent satellite observations have shown that a horizontal divergent flow (HDF) stretches out over the solar surface just before the magnetic flux appearance. Aims. The aims of this study are to investigate the driver of the HDF and to see the dependency of the HDF on the parameters of the magnetic flux in the convection zone. Methods. We conducted three-dimensional magnetohydrodynamic (3D MHD) numerical simulations of the magnetic flux emergence and varied the parameters in the initial conditions. An analytical approach was also taken to explain the dependency. Results. The horizontal gas pressure gradient is found to be the main driver of the HDF. The maximum HDF speed shows positive correlations with the field strength and twist intensity. The HDF duration has a weak relation with the twist, while it shows negative dependency on the field strength only in the case of the stronger field regime. Conclusions. Parametric dependencies analyzed in this study may allow us to probe the structure of the subsurface magnetic flux by observing properties of the HDF