CHEN Hechao, a PhD student from Yunnan Observatories of Chinese Academy of Sciences, has reported a new phenomenon in The Astrophysical Journal recently. He and his collaborators find that the line-tied footpoints of erupting magnetic flux ropes (MFRs) can drift to new location during its eruption. This new result implies that mapping the real footpoints of the erupting MFR down to the solar surface is more difficult than solar physics scientists previously thought.

Coronal mass ejections (CMEs) are well-known drivers for most extreme energetic space weather in our solar system. These large-scale solar eruptive activities originate from the loss-of-equilibrium of solar magnetic flux ropes, and may easily make our near-Earth space a hazardous place. Mapping the real footpoints of erupting CME flux ropes down to the solar surface is the key to build the physical links between solar eruption and their resulting enegertic space weather.

Core dimmings, the transient dark regions that appeared during the early eruption phase of CMEs, often conjugately present at the extremes of flare ribbons. Thus, they have been tentatively explained as the line-tied footpoints of the evacuated CME flux ropes. At present, in many observational works, this tentative assumption has been used as a basic condition to estimate the mass supply and poloidal flux of CME flux ropes. However, whether this tentatively assumption is reliable remains unclear.

With the joint observations from New Vacuum Solar Telescope (NVST) and Solar Dynamic Observatory (SDO), CHEN and his coauthors conduct a detailed observational analysis on the early evolution of a CME flux rope in NOAA active region 12010. They find that MFR’s footpoints underwent a dynamical drift near both core dimmings. In particular, MFR’s west footpoint drift is proved to be induced by a new reconnection geometry among the erupting MFR’s leg and thereby inclined arcades. As MFR’s west footpoints drifted to a new position, a set of newborn atypical flare loops connected into the west core dimming, causing a rapid decrease of dimmed area inside this core dimming.

"This new-found footpoint drift phenomenon in our research now clearly reveals that core dimmings indeed can't accurately map the real footpoints of the erupting CME flux rope in some real eruption events. To better solve this problem, a more rigorous and reliable approach is required in the future”, CHEN said.

Contact:

CHEN Hechao, Yunnan Observatories, CAS

chc@ynao.ac.cn