Magnetic Structure Responsible for Coronal Disturbances: Theory

Abstract

Due to the strong coupling between the coronal material and magnetic fields, magnetic structures are probably intimately involved, either actively or passively, in virtually all coronal disturbances. The purpose of this paper is to put into perspective the various roles magnetic fields can play in both exciting and guiding these observed transient phenomena. A discussion of our present theoretical concepts relevant to this subject can be conveniently divided into four categories. We begin by discussing our present understanding of how the gross magnetic structure of the corona is determined. Important considerations here are the tendency for the coronal field to seek its lowest energy state, the effect of convection on the field, and the influence of the solar wind. Secondly, we investigate magnetic structures which reside in elevated energy states (higher than the energy of an equivalent potential field) as well as disturbances which appear to be related to changes in these configurations. Thirdly, the role of the field in guiding coronal disturbances is considered. This is evident for bulk motions (sprays, surges, flare loops, green line events, etc.), wave motions (flare associated waves, Alfvén waves), as well as for individual particle phenomena. Lastly, a special class of magnetic structures which seem to be constantly associated with coronal activity are discussed. These are the magnetic discontinuities such as neutral sheets and current sheets. In this context, the magnetic neutral point and associated reconnection phenomena are considered.