Evolution of the Mid-Latitude Red Aurora Over Northern China During the 5 November 2023 Geomagnetic Storm

Abstract

This study presents novel observations of a mid-latitude red aurora event at 44°MLAT over Northern China during the 5 November 2023 geomagnetic storm, using simultaneous observations from ground-based instruments (630 nm all-sky imager (ASI) and ionosonde) at Mohe station (53.5°N, 122.4°E; MLAT = 44.32°N) and space-based satellites (Swarm and Defense Meteorological Satellite Program F17 and F18). The auroras displayed unusual dynamics, appearing north of the ASI field of view (FOV) at 1000 UT, disappearing at 1300 UT, then reappearing at 1400 UT with equatorward expansion (∼62 m/s) to reach 51°N (42°MLAT/2.3 L) and lasting ∼8 hr. Analysis indicated that the auroral characteristics resembled stable auroral red arc (SARc), including thermal excitation (electron temperatures >3,000 K) and ionogram features (weak spread-F occurrence and reduced critical frequency). The auroras exhibited distinctive yet previously unreported properties of SARc, prompting their definition as SARc-like events. Specifically, the auroral emissions demonstrated clear additional contributions from ion precipitation (hundreds eV to tens keV ions) alongside thermal excitation of the typical SAR theory, and they were not fixed within the ionospheric trough unlike a narrow band of typical SARc pattern. The ionospheric trough at its equatorward edge exhibited synchronous equatorward motion. Concurrently, ionosonde echoes weakened and disappeared as the aurora and trough passed overhead, suggesting density depletion effects. Both the trough dynamics and ion precipitation likely drove electron temperature enhancements. These findings reveal new complexities in mid-latitude auroral physics requiring further investigation.