Evolution of the toroidal flux of solar coronal mass ejections derived by tracing their on-disk footpoints

As the most violent large-scale explosive phenomenon in the solar atmosphere, coronal mass ejections (CMEs) are the main source of disastrous space weather in our solar-terrestrial environment. Detailed evolution of the toroidal magnetic flux inside CME flux ropes is still poorly understood. Recently, researchers from Nanjing University developed a new method to achieve a better identification of the footpoint regions of erupting CME flux ropes. Applying this new method, they successfully obtained and further quantitatively investigated the evolution of toroidal flux of four erupting flux ropes. They found that the toroidal flux of CME flux ropes experiences a rapid increasing phase followed by a decreasing phase. Such a two-phase evolution of toroidal flux is generally synchronous with the energy release process in CME-associated solar flares. This study provides a quantitative assessment of the variation of the toroidal flux of CME flux ropes during their eruptions, which is of vital significance for understanding the three-dimensional nature of CMEs.