Dynamic Component Reconnection and FTE-Driven Electron-Scale Processes under Large Dipole Tilt: A Multi-Spacecraft Study

We investigate the dynamics of magnetopause component reconnection under extreme winter solstice conditions with a dominant IMF-By component. Joint observations from ACE (at L1 point) and THEMIS-D (near the bow shock) reliably confirmed the solar wind conditions. At the low-latitude magnetopause, MMS observed multiple ion flow reversals within 7 minutes, indicating a dynamic component reconnection X-line topology. The component X-line’s central segment position deviates from Maximum Magnetic Shear model predictions. Consistent with previous research by Trattner et al., we demonstrate that under specific conditions, component X-lines are controlled by the interplay between the antiparallel reconnection region and magnetic shear maximization. On the kinetic scale, MMS detected two ion-scale flux transfer events (FTEs) with identical L-direction velocity but opposite helicity. The anomalous helical FTE1 was entirely located on the magnetosheath side, leading to a steep magnetic field gradient at the pressure-balanced interface between FTE1 and the magnetopause. In this region, MMS observed super-Alfvénic electron flows and varying electron agyrotropy but lacked classical EDR (electron diffusion region) signatures. We propose this represents an electron-only reconnection initiation mediated by diamagnetic current, triggered by the anomalous helical FTE contacting the magnetopause, rather than a traditional secondary reconnection site. Our study provides observational evidence for dynamic component reconnection and identifies a new mechanism for electron-only reconnection onset driven by diamagnetic currents.