Model calculation of the N2+ first negative intensity and vibrational enhancement from energetic incident O+ energy spectra

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Abstract
The N2+ first‐negative band system with high vibrational and rotational enhancement appears in the midlatitude region during large geomagnetic storms and its (0–0) band emission intensity ranges up to 1000 Rayleighs (R). The observed ratios of the (1–1) to (0–0) bands are high (8%–22%) compared to the value of 4.5% for electron auroras excited by keV electrons. The ratio of the (2–2) to (0–0) bands is more than an order of magnitude larger than that in the case of electron aurora. Analysis of the observed ground based spectra has led to the conclusion that energetic O+ precipitation causes the midlatitude emissions. We investigated whether energetic O+ could produce the N2+ 1N (0–0), (1–1) and (2–2) band emissions with similar intensities and ratios to those observed at midlatitude. An O+ transport model with measured N2+ 1N cross sections calculated the emissions with variation in several parameters: the incident O+ spectra, scattering cross sections, and the model atmosphere. The results indicate that 1) the majority of the O+ must have energies below 10 keV to produce the observed vibrational enhancement, and 2) the total energy flux must be on the order of 10 erg cm−2 s−1. Such energy flux would also cause peak atmospheric heating a factor of three larger than that due to the noon solar extreme ultraviolet energy deposition.