Solar Coronal Magnetic Field Research Articles

Models of partially open magnetospheres with and without magnetodisks

This paper presents a large class of analytic solutions describing partially open magnetic fields in static equilibrium outside a central object, which may be taken to be a planet or a star. The problem for a potential magnetic field is first treated in axisymmetric geometry, with an equatorial, stress-free electric current sheet whose presence results in part of the magnetic flux opening to infinity. The solutions can be linearly superposed to construct idealized models of the solar coronal magnetic field in a partially open configuration. These solutions are further developed to allow for stresses in the current sheet and three-dimensionality, in that order of complexity. The stresses can be balanced in equilibrium by introducing gravitational and centrifugal forces acting on dense matter confined in the electric current sheet. Explicit solutions are presented to illustrate magnetic topologies of magnetospheres having rotating and nonrotating magnetodisks. A simple physical illustration is given to estimate the total mass in the Jovian magnetodisk from the observed macroscopic parameters of the disk electric current. 21 references.

Magnetic stability of coronal arcades relevant to two-ribbon flares

The dense photosphere provides an extremely efficient mechanism, called line-tying, for stabilising solar coronal magnetic fields. In this paper, we study the ideal magnetohydrodynamic (MHD) stability of cylindrically symmetric arcades, the field structure thought to be present prior to the onset of a large two-ribbon flare. It is found that, when the axis of symmetry lies on the photosphere, a wide range of force-free fields are completely stable to all possible perturbations. However, replacing the axial magnetic field by an equivalent gas pressure will produce a localised instability. Instability, the mechanism for the release of energy for a flare, will also occur if the symmetry axis, assumed to coincide with an active-region filament, is too high above the photosphere to benefit from its stabilising influence.

Large Scale Variations in Solar Coronal Density and Magnetic Fields

Observations of the solar equatorial electron scattered coronal radiance made during the Skylab mission show characteristics which dramatically differ with time. The results may be interpreted as indicating a general simplification of the coronal magnetic field, and, in comparison with harmonic analysis of observed solar surface magnetic fields, as indicating a rapid response of outer coronal structures to abrupt changes in the global solar surface field structure.