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

Abstract

This study presents a first simultaneous observation of N2+ Meinel (0,0) band (hereafter, N2+(M)) aurora by cutting-edge short wavelength infrared imaging spectrograph (NIRAS-2) and monochromatic camera (NIRAC) installed at Kjell Henriksen Observatory (78ºN, 16ºE). On January 21 2023, N2+(M) intensification of associated with a band-shape aurora structure was observed by the NIRAS-2 and the NIRAC by temporal resolutions of 30 seconds and 20 seconds, respectively. Additionally, the European incoherent scatter Svalbard Radar also observed electron density variations at the same time. Electron density measured at altitude ranges from 100 km 120 km changed in the same way as N2+ (M) intensity, which implies that a primary source of N2+ (M) emissions is direct collisions of N2 by precipitating electrons penetrating down to around 100 km altitude (up to 10 keV). However, the observation also demonstrated moderate correlations between N2+ (M) intensity and electron density above 140 km, which implies that different N2+(M) generation process, N2 charge exchange with O+, may work up to near 160 km and make a non-negligible contribution to N2+(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+ (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+ (M) characteristics, for future missions of both balloon-borne and satellite-borne imaging.