Magnetic Field Confinement in the Solar Corona. II. Field‐Plasma Interaction

Abstract

The numerical study of axisymmetric force-free magnetic fields in the unbounded space outside a unit sphere, presented in the first paper of this series, is extended to treat twisted fields in static equilibrium with plasma pressure and weight in a polytropic atmosphere. The study considers dipolar magnetic fields all sharing the same boundary flux distribution on the unit sphere and characterized with (a) a nonlinear distribution of its azimuthal field component expressed as a power of the poloidal flux function and (b) a plasma distribution varying linearly with the poloidal flux function. Nonlinear boundary value problems are solved numerically to generate a continuum of solutions with two parameters to control the total azimuthal flux and the strength of field-plasma interaction. The study includes the force-free fields of the first paper as a special case. Models with polytropic indices Γ = 7/6, 14/11 are treated to show the interplay between the degree of magnetic twist and hydrostatic stratification in determining atmospheric structures, with particular interests in magnetic flux ropes and their storage of magnetic energy and azimuthal flux at levels above those bounds applicable to force-free fields. The concluding discussion relates physical insights from the study to the solar corona and the energetics of coronal mass ejections and flares. Subject headings: magnetohydrodynamics: Sun, solar prominences, solar coronal mass ejections, solar corona