New Physical Insight on the Changes in Magnetic Topology during Coronal Mass Ejections: Case Studies for the 2002 April 21 and August 24 Events
In order to investigate the dynamics of the coronal mass ejections on 2002 April 21 and August 24, we performed a series of numerical simulations with an ad hoc driver for the eruptions. The resulting evolution of the solar corona for each event was followed by means of three-dimensional MHD simulations. We used SOHO MDI data to set realistic boundary conditions for the ambient magnetic field of the Sun. In our model, the loss of equilibrium of the coronal magnetic field and subsequent eruption were achieved by stretching the opposite polarity feet of a newly emerged magnetic dipole. The stressed magnetic field reconnects through null points and, in the case of the August 24 event, also through a quasi-separator. As a result, magnetic flux and helicity are transferred from the expanding flux system containing the evolving dipole to the nearby flux systems. Another result is the jumplike change in the location of one footprint of the erupting magnetic field. This Letter emphasizes the importance of studying CMEs on a case-by-case basis if we are to understand their dynamics, energetics, and interplanetary consequences.