The role of flux emergence as a driver of coronal mass ejections

Recently it has been suggested that coronal mass ejections (CMEs) are closely related to the interaction between different magnetic domains formed in the corona. For example, a so-called breakout model of CMEs shows that a core domain field which is enhanced by shearing motions in the photosphere interacts with the overlying field, and this weakens the confining effect of the overlying field and eventually enables the core domain field to erupt outwards. In this study, we take the subphotospheric dynamics into this model and see how flux emergence affects the breakout process. Our work is based on 3-dimensional resistive MHD simulations in which we initially set a potential bipolar field above the photosphere and place a magnetic flux tube below the photosphere. The flux tube then emerges into the photosphere and starts to interact with the bipolar field. As the flux tube expands into the corona, a current layer develops around the interface between emerging magnetic field and preexisting coronal field. We focus on its structure and evolution because that current layer plays a crucial role in a breakout of emerging magnetic field. To see this, we apply a locally enhanced resistivity around the current layer and study the magnetic reconnection between emerging field and preexisting field.