Interaction of Coronal Material with Magnetic Fields

Abstract

The optical resolution in recent eclipse photographs is now sufficient to illustrate clearly many qualitative features of gas-magnetic field interactions in the solar corona. Close to the Sun where the field is strong, the coronal gas over certain regions of the solar surface can be contained within closed loop structures. However, since the field strength in these regions declines outward rapidly, the pressure and inertial forces of the solar wind eventually dominate and distend the field outward into interplanetary space. The overall configuration is determined by a complex interplay of inertial, pressure, gravitational, and magnetic forces. The present work is oriented toward the understanding of this interaction.Of central importance to this general problem is the typical ‘helmet’ streamer generally overlying a large diffuse bipolar region on the solar surface. A helmet streamer consists of closed magnetic loops near the Sun and open field lines adjacent to and above the loops. The configuration possesses a ‘cusp-type’ neutral point (to be differentiated from a y-type neutral point) at the top of the closed loops. In addition to volume currents, a single sheet current separates the regions of opposite polarity above the neutral point. Below the neutral point, sheet currents also are present between the open and closed regions. These sheet currents are necessary to support the discontinuity in gas pressure which arises since the open region is expanding and the closed region is not. The neutral point problem is discussed in some detail and sample numerical examples are presented.