MMS Observations of Storm‐Time Magnetopause Boundary Layers in the Vicinity of the Southern Cusp

During a storm‐time interval around winter solstice, observations by the Magnetospheric Multi‐Scale (MMS) Mission show multiple distinct magnetopause boundary layers (BLs) in the vicinity of the southern cusp. The microphysics of the solar wind‐magnetosphere interaction during storm times are not well understood, because the observations are relatively lacking. This event enables the opportunity to probe the storm‐time magnetopause, and observations support that MMS was near a reconnection site equatorward of the southern cusp, suggesting active reconnection in close proximity to closed magnetic flux regions in the BL. The Grid Agnostic magnetohydrodynamics (MHD) for Extended Research Applications global MHD simulation shows evidence for transient secondary reconnection sites near the southern cusp, demonstrating mechanisms to form closed field line regions of the BL.