Role of Closed Magnetic Fields in Solar Wind Flow

Abstract

In this paper we demonstrate how closed magnetic fields appear to be playing a significant role in solar wind flow. Confinement or trapping of plasma is the physical process, while confinement duration, as characterized by the first ionization potential (FIP) bias, is the attribute that divides the fast- and slow-wind regions. The trapped plasma is released along ubiquitous and predominantly radial open field lines, presumably by continual reconnection at the base of the corona, with evidence for this process coming from the appearance of the imprint of polar coronal holes, quiet Sun, and active regions in the outer corona and interplanetary space. When trapping is not long enough to enrich the elemental abundance (FIP bias near 1), the coronal radial density gradient is steep, coronal temperature is low, and a fast wind flows in the overlying corona. However, the presence of closed fields still influences the flow of the fast wind, as revealed by the fact that flow speed is anticorrelated with, or characterized by, the density at the base of the corona. When trapping is long enough to enrich the abundance (FIP bias > 1), a slow wind flows, and FIP bias characterizes its properties. Enhanced FIP bias gives rise to a decreased coronal radial density gradient, as manifested by the extension of coronal streamers in white-light coronal images, increased coronal temperature, and decreased solar wind speed in the overlying corona.