The Triple-layered Leading Edge of Solar Coronal Mass Ejections

Abstract In a high-resolution, 3D resistive magnetohydrodynamic simulation of an eruptive magnetic flux rope (MFR), we revisit the detailed 3D magnetic structure of a coronal mass ejection (CME). Our results highlight that there exists a helical current ribbon/boundary (HCB) that wraps around the CME bubble. This HCB results from the interaction between the CME bubble and the ambient magnetic field, where it represents a tangential discontinuity in the magnetic topology. Its helical shape is ultimately caused by the kinking of the MFR that resides within the CME bubble. In synthetic Solar Dynamics Observatory/Atmospheric Imaging Assembly images, processed to logarithmic scale to enhance otherwise unobservable features, we show a clear triple-layered leading edge: a bright fast shock front, followed by a bright HCB, and within it a bright MFR. These are arranged in sequence and expand outward continuously. For kink unstable eruptions, we suggest that the HCB is a possible explanation for the bright leading edges seen near CME bubbles and also for the non-wave component of global EUV disturbances.