THE ROLE OF MAGNETIC RECONNECTION IN THE OBSERVABLE FEATURES OF SOLAR ERUPTIONS

摘要

There are two competing classes of models for coronal mass ejections (CMEs): those that assume a preexisting magnetic flux rope and those that can make a flux rope during the eruption by magnetic reconnection. The present work is based on the model with a preexisting flux rope. We investigate the evolution of morphological features of the magnetic configuration in a CME according to a catastrophe model of flux rope CMEs developed previously. For the parameters chosen for the present work, roughly half of the total mass and magnetic flux are contained in the initial flux rope, while the remaining plasma and poloidal magnetic flux are brought by magnetic reconnection from the corona into the current sheet and from there into the CME bubble. These features and the corresponding physical processes are identical to those described by the non-flux rope models. Thus, the flux rope and non-flux rope models are less distinct than is generally assumed. The reconnected magnetic flux can account for the rapid expansion of the ejecta, and the plasma flowing out of the current sheet fills the outer shell of the ejecta. We tentatively identify the outer shell, the expanded bubble, and the flux rope with the leading edge, void, and core of the three-component CME structure, respectively. Thus, the final mass, speed, and magnetic energy―the quantities that determine the geoeffectiveness of the CME―are determined not in the initial eruption but during the CME expansion, at heights of a few solar radii. The aspects of this explanation that need improvement are also discussed.