Formation of Magnetic Flux Rope During Solar Eruption. I. Evolution of Toroidal Flux and Reconnection Flux

Magnetic flux ropes (MFRs) constitute the core structure of coronal mass ejections (CMEs), but hot debates remain on whether MFR forms before or during solar eruptions. Furthermore, how flare reconnection shapes erupting is still elusive in three dimensions. Here we studied a new MHD simulation CME initiation by tether-cutting magnetic single arcade. The follows whole life, including birth and subsequent evolution, an eruption. In early phase, partially separated from its ambient field quasi-separatrix layer (QSL) that has double-J shaped footprint bottom surface. With ongoing reconnection, arms two J-shaped footprints continually separate each other, hooks J expand eventually become closed almost at eruption peak time, thereafter fully un-reconnected QSL. We further evolution toroidal compared it with reconnected flux. Our reproduced pattern increase-to-decrease flux, which reported recently observations variations ribbons transient dimming. increase owing to phase transforms sheared arcade twisted lines, while decrease result between lines interior later phase.