GHOST aurora – continuum emission produced by hot N₂

Abstract. We investigate the origin of the continuum emissions observed in the poleward boundary dayside aurora discovered in Partamies et al. 2025, known as GHOST, and propose that they arise from highly excited, hot N₂. Using spectral modelling and fits to ground-based measurements of high-resolution GHOST spectra, we demonstrate that vibrationally and rotationally excited N₂ and N₂⁺ can reproduce the observed structured continuum without requiring emission from NO. Spectral fitting indicates that GHOST events coincide with extreme ion heating and high neutral temperatures. Background conditions from additional events indicate that strong ionospheric flows are typically present, which can help to provide the necessary energy input for producing hot neutral and ionised N₂. Proton aurora observations and EISCAT incoherent scatter radar measurements of ionospheric plasma parameters indicate that two of our three events are located in the cusp. These results suggest that the combination of strong flow, heating, particle precipitation, and cusp conditions produce thermally excited N₂ populations which can account for the continuum spectrum of GHOST.