The significance of resonant scatter in the measurement of N2+ first negative 0-1 emissions during auroral activity

Ionized nitrogen molecules are readily created by incoming primary and secondary electrons during auroras. Photometric measurements of emissions in the first negative system, which originates from the B state, have been widely used to make an estimate of the energy flux of precipitating electrons. Some emissions from the A state of ionized molecular nitrogen occur in the meinel bands in the near infrared. In this study we have compared simultaneous observations of the first negative system in the 0-1 band with the Meinel 0-0 band during aurora at Poker Flat, Alaska. Since both upper states have short lifetimes, compared to the inverse of the collision rate at heights of the emission, and the ratios of their excitation cross sections by electron impact is not sensitive to energy above 10 eV, it was expected that their emission rates should be strictly proportional. We have found that the brightness of the first negative 0-1 increases above the proportionality rate during moderate auroral activity. After careful consideration of a number of possible causes, this increase is credited to the resonant scattering of the first negative emission due to a possible elevation of N-2(+) into the sunlit or twilight region. (C) 2001 Elsevier Science Ltd. All rights reserved.