Magnetohydrodynamic simulation of non–flux rope coronal mass ejections

Abstract

Observations at 1 AU indicate that only 1/3 of coronal mass ejections (CMEs) have a flux rope structure, while the other 2/3 of CMEs have a complex disordered magnetic field. The initiation of the flux rope CMEs has been extensively simulated with various magnetohydrodynamic (MHD) models. However, the initiation of the non–flux rope CMEs is rarely done in numerical modeling. In this paper, we numerically simulate the physical origin and characteristics of the non–flux rope CMEs by using a three‐dimensional, axisymmetric, time‐dependent, self‐consistent MHD model. The results show that the emergence of a counterclockwise flux rope from the lower coronal boundary at the open magnetic field region, near the closed magnetic field lines, can initiate a magnetic configuration, which causes the magnetic reconnection at the coronal base. Physically, the magnetic field of the emerged counterclockwise flux rope has antipolarity with the background open field, and the location of the magnetic flux emergence is at the edge of a coronal hole. This magnetic reconnection between closed and open field lines at the coronal base generates an Alfvénic jet‐like plasma outflow. It could further develop into a non–flux rope CME if enough magnetic energy is deposited. Solar energetic particle (SEP) events in association with the non–flux rope CMEs are usually impulsive because the magnetic topology obtained from this simulation of non–flux rope CMEs corresponds to that proposed by Reames (2002) to lead impulsive SEP events.