Ionospheric currents and auroral signatures during successive earthward bursty bulk flows and dipolarization: a 7 December 2023 case study

Earthward bursty bulk flows (BBFs) in the central plasma sheet are frequently accompanied by dipolarization fronts, and together they account for a large fraction of the energy and momentum transported from the magnetotail to the high-latitude ionosphere through field-aligned currents (FACs). On 7 December 2023, between 18:00 and 22:00 UT, six BBFs-intervals were detected by THEMIS, with clear dipolarization signatures in the last four intervals. These flows map to the pre-midnight magnetic local time sector over northern Fennoscandia, where the ionospheric response is examined using horizontal equivalent current density derived from the IMAGE magnetometer network and auroral emissions from all-sky cameras. At the beginning of the interval, the ionospheric current system exhibits a stable Harang discontinuity, which becomes progressively distorted after each BBF and ultimately evolves into a clear westward electrojet. The first two dipolarizing intervals are accompanied by auroral pseudo-breakups, whereas the final two display an auroral breakup and poleward expansion characteristic of substorms. A key interval occurs during the fourth BBF, whose mapped footpoint intersects the Swarm A/C orbit and reveals a strongly localized pair of upward and downward FACs spanning 35–50 km in latitude, with the upward current colocated with a discrete auroral arc. Throughout the BBF activity, the horizontal ionospheric current density reorganizes rapidly around the mapped footpoints, and the auroral arc intensifies simultaneously with THEMIS enhancements of 9–20 keV electron fluxes. These observations demonstrate that localized magnetotail flows can drive fast, structured, and cumulative modifications of the ionospheric electrodynamics, emphasizing the importance of multi-point measurements for resolving the temporal evolution of magnetosphere–ionosphere coupling during BBFs.