The first simultaneous spectroscopic and monochromatic imaging observations of short-wavelength infrared aurora of N₂⁺ Meinel (0,0) band at 1.1 μm with incoherent scatter radar

This study presents a first simultaneous observation of N₂⁺ N 2 + Meinel (0,0) band (hereafter, N₂⁺ N 2 + (M)) aurora by cutting-edge short-wavelength infrared imaging spectrograph (NIRAS-2) and monochromatic camera (NIRAC) installed at the Kjell Henriksen Observatory (78 ^∘ ∘ N, 16 ^∘ ∘ E). On January 21 2023, N₂⁺ N 2 + (M) intensification that is associated with a band-shape aurora structure was observed by the NIRAS-2 and the NIRAC having temporal resolutions of 30 s and 20 s, respectively. In addition, the European incoherent scatter Svalbard Radar also observed electron density variations at the same time. Electron density measured at altitude range from 100 km 120 km shows similar variations as of N₂⁺ N 2 + (M) intensity, which implies that a primary source of N₂⁺ N 2 + (M) emissions is direct collisions of N₂ N 2 by precipitating electrons penetrating down to around 100 km altitude (up to 10 keV). However, the observation also demonstrated moderate correlations between N₂⁺ N 2 + (M) intensity and electron density above 140 km, which implies that different N₂⁺ N 2 + (M) generation process, N₂ N 2 charge exchange with O⁺ O + , may work up to near 160 km and make a non-negligible contribution to N₂⁺ N 2 + (M) emissions. This hypothesis would be verified with further radar observations or stereo imaging observations useful to estimate the vertical distribution of the emission layers. The N₂⁺ N 2 + (M) is a very promising target wavelength for aurora observation because the quality of sensors is highly expected to improve further and further. Continuous observations with our new instruments will undoubtedly provide an important information of N₂⁺ N 2 + (M) characteristics, for future missions of both balloon-borne and satellite-borne imaging.