A night-side shock aurora and its three different emissions observed on 26 February 2023

Ground-based observations of shock aurora, which is an aurora related to geomagnetic sudden commencement (SC), have mainly been limited to the dayside. On 26 February 2023, right after the SC onset at 19:24 UT, ground-based all-sky cameras and a wide-angle camera detected shock aurora at 21 MLT in the auroral zone. For this aurora, three different emissions are detected instead of the previously known two emissions: intensification of a pre-existing arc (19:25 UT), red diffuse aurora (19:28 UT), and a second, green discrete arc (19:31 UT). The relative location of these emissions differs from the dayside cases where the first and last types are not distinguished. Geomagnetic data under this aurora indicates a significant difference in the anti-sunward propagation velocity between the secondary discrete arc and the related field-aligned current.