The Origin of Core Magnetic Structures in Solar Eruptions: Theoretical Concepts and Numerical Models

This overview will first characterize the two relevant core magnetic structures of solar eruptions, sheared arcade and flux rope, including the aspects of current neutralization and flux rope topology. Following a brief account of the origins of shear, the focus will lie on the formation of flux ropes, where flux emergence and rotating sunspots contribute but reconnection in the atmosphere appears to be the dominant process. We compare reconnection associated with flux cancellation, with tether cutting and with confined eruptions, which are topologically equivalent but have different drivers and time scales. This leads to a discussion of the key question whether a flux rope forms before or after eruption onset. Many observations and numerical studies indicate that flux ropes begin to form prior to eruption but often remain incoherent, i.e., mixed with sections of arcade type, until or nearly until a full and ejective eruption of the current-carrying flux commences.