Three-dimensional magnetohydrodynamic simulation of the solar magnetic flux emergence: Parametric study on the horizontal divergent flow

TL;DR

This study uses 3D MHD simulations and analytical methods to investigate the drivers and parameter dependencies of horizontal divergent flows associated with solar magnetic flux emergence, revealing pressure gradients as key drivers and correlations with flux properties.

Contribution

It provides new insights into the physical drivers of HDF and how its characteristics depend on magnetic flux parameters, aiding subsurface magnetic structure probing.

Findings

Horizontal pressure gradient drives HDF.

HDF speed correlates with magnetic field strength and twist.

HDF duration weakly depends on twist, negatively on field strength in strong fields.

Abstract

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. 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. We conduct three-dimensional magnetohydrodynamic (3D MHD) numerical simulations of the magnetic flux emergence and vary the parameters in the initial conditions. An analytical approach is also taken to explain the dependency. 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. Parametric dependencies analyzed in this study may allow us to probe the structure of the subsurface magnetic flux by observing properties of the HDF.