The 2003 October–November Fast Halo Coronal Mass Ejections and the Large‐Scale Magnetic Field Structures

Abstract

The coronal magnetic field, computed from synoptic maps of the magnetic field and a potential field source surface (PFSS) model, reveals special configurations related to the active regions that were associated with most, if not all, fast halo coronal mass ejections (CMEs) in 2003 October-November. It was shown that these active regions emerged in an open field area, produced a large open field area after emerging, or sat on a boundary of two open field areas with the same polarity. This type of boundary is also known as a "plasma sheet." Such magnetic structures appear to be favorable for the propagation of the disturbance. MHD simulations were performed here to explore the behavior of the propagation of the disturbance against these special configurations of the background magnetic field. It is demonstrated that without the presence of open flux, the speed of the CMEs would have been only 78% of that with open flux present. It is also found that the CMEs from a heliospheric current sheet have a speed only 67% of the CMEs' speed from a plasma sheet, the source boundary with the same polarity.