Near-Earth Reconnection Contributing to Recovery Phase of Geomagnetic Storm

Recent observations show very near-Earth reconnection (similar to 8-13RE) could efficiently power the ring current during the main phase of geomagnetic storms, but whether the recovery phase might be contributed remains unclear. During the recovery phase of the May 2024 major geomagnetic storm, intense auroral brightening and geomagnetic disturbances were observed at midnight, indicative of particle injections. Current wedges observed by mid-latitude ground magnetometers around midnight suggest dipolarizing flux bundles (DFBs). The latitude of the auroral brightening was clearly lower than usual, suggesting near-Earth reconnection (NERX) was closer to Earth than during substorms (similar to 20-30RE). GOES-18 at midnight detected magnetic field and plasma signatures consistent with DFBs, following an extremely thin current sheet likely compressed by strong upstream dynamic pressure. These results indicate NERX could have been close enough for resultant DFBs to penetrate geosynchronous orbit and contribute to the ring current during the recovery phase. This scenario deserves further examination in future.