Magnetic configurations related to the coronal heating and solar wind generation. I. Twist and expansion profiles of magnetic loops produced by flux emergence

摘要

The generation of outflows from the Sun known as solar winds is coupled with the heating of the solar corona, and both processes are operated in magnetic structures formed on the Sun. To study themagnetic configuration responsible for these processes, we use three-dimensional magnetohydrodynamic simulations to reproduce magnetic structures via flux emergence and investigate their configurations. We focus on two key quantities characterizing a magnetic configuration: the force-free parameter α and the flux expansion rate f_(ex), the former of which represents how much a magnetic field is twisted while the latter represents how sharply amagnetic field expands.We derive distributions of these quantities in an emerging flux region. Our result shows that an emerging flux region consists of an outer part where a magnetic loop takes a large flux expansion rate but a small value of α at their photospheric footpoints, and an inner part occupied by those loops where a strong electric current flows. We also investigate the expansion profile of a magnetic loop comprising an emerging flux region. The profile is given by an exponential expansion type near the solar surface while it is given by a quadratic expansion type in an outer atmosphere. These detailedmagnetic configurations obtained by this study contribute to developing a realistic model for the coronal heating and solar wind generation.