Hwanhee Lee

HALF-TURN ROTATION OF A POLARITY INVERSION LINE AND ASSOCIATED QUADRUPOLAR-LIKE STRUCTURE IN THE SUN

This paper reports a characteristic motion of a polarity inversion line (PIL) formed at the solar surface, which is newly found by performing a three-dimensional magnetohydrodynamic simulation of flux emergence in the Sun. A magnetic flux tube composed of twisted field lines is assumed to emerge below the surface, forming a bipolar region with a PIL at the surface. A key finding is the successive half-turn rotation of the PIL, leading to the formation of a quadrupolar-like region at the surface and a magnetic configuration in the corona; this configuration is reminiscent of, but essentially different from the so-called inverse-polarity configuration of a filament magnetic field. We discuss a physical mechanism for producing the half-turn rotation of a PIL, which gives new insights into the magnetic structure formed via flux emergence. This presents a reasonable explanation of the configuration of a filament magnetic field suggested by observations.

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

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 the magnetic 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 alpha and the flux expansion rate fex, the former of which represents how much a magnetic field is twisted while the latter represents how sharply a magnetic field expands. We derive distributions of these quantities in an emerging flux region. Our result shows that an emerging flux region consists of outer part where a magnetic loop takes a large flux expansion rate but a small value of alpha at their photospheric footpoints, and inner part occupied by those loops where a strong electric current flows. We also investigate the expansion profile of a magnetic loop composing 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 detailed magnetic configurations obtained by this study contribute to developing a realistic model for the coronal heating and solar wind generation.