The automatic identification and tracking of coronal flux ropes I. Footpoints and fluxes

Context. Investigating the early-stage evolution of an erupting flux rope from the Sun is important for understanding the mechanisms of how it loses its stability and its space-weather impact. Aims. Our aim is to develop an e fficient scheme for tracking the early dynamics of erupting solar flux ropes and to use the algorithm to analyse its early-stage properties. The algorithm is tested on a data-driven simulation of an eruption that took place in active region AR12473. We investigate the modelled footpoint movement and magnetic flux evolution of the flux rope and compare these with observational data from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) in the 211 angstrom and 1600 angstrom channels. Methods. We used the time-dependent data-driven magnetofrictional model (TMFM) to carry out our analysis. We also performed another modelling run, where we stop the driving of the TMFM midway through the rise of the flux rope through the simulation domain and evolve it instead with a zero-beta magnetohydrodynamic (MHD) approach. Results. The developed algorithm successfully extracts a flux rope and its ascent through the simulation domain. We find that the movement of the modelled flux rope footpoints showcases similar trends in both the TMFM and relaxation MHD runs: the footpoints recede from their respective central location as the eruption progresses and the positive polarity footpoint region exhibits a more dynamic behaviour. The ultraviolet (UV) brightenings and extreme ultraviolet (EUV) dimmings agree well with the models in terms of their dynamics. According to our modelling results, the toroidal magnetic flux in the flux rope first rises and then decreases. In our observational analysis, we capture the descending phase of toroidal flux. Conclusions. The extraction algorithm enables us to e ffectively study the early dynamics of the flux rope and to derive some of its key properties, such as footpoint movement and toroidal magnetic flux. The results generally agree well with observational data.