Analyzing the Geomagnetic Impact of Interacting CMEs and Sector Boundary Crossings During Autumn 2023 Eruptive Events

This study comparatively investigates two sets of eruptive solar events in late 2023 which occurred in two episodes with similar eruption characteristics, separated by a full solar rotation. The solar activity periods cover October 31–November 3 and November 27–28. Both episodes were linked to intense geomagnetic storms, on November 4–5 and December 1–2, respectively, with strongest effects on November 5. In detail we find that the first episode produced visible Stable Auroral Red (SAR) arcs and a three-step decline in the Dst index to −163 nT. This event involved two CME-related shocks, a sector boundary crossing (SBC), and a short-duration flux rope. The second episode led to auroral lights and a two-step Dst index drop to −108 nT, featuring a shock within another CME's magnetic structure, combined with a SBC and a clear flux rope structure. Both events displayed short-term magnetic field variations and fluctuations in density and temperature post-SBC.

Our comparative analysis highlights the role of interacting CME structures, and the modulation effects of magnetic structures related to SBCs, contributing to the stronger geomagnetic impact observed in the November 4–5 event. Additionally, the highly tilted orientation of the heliospheric current sheet likely intensified the interactions with the CMEs, enhancing their geomagnetic influence.