The significance of resonant scatter in the measurement of N-2(+) first negative 0-1 emissions during auroral activity

Ionized nitrogen molecules are readily created by incoming primary and seco ndary electrons during auroras. Photometric measurements of emissions in th e first negative system, which originates from the B state, have been widel y used to make an estimate of the energy flux of precipitating electrons. S ome emissions from the A state of ionized molecular nitrogen occur in the m einel bands in the near infrared. In this study we have compared simultaneo us observations of the first negative system in the 0-1 band with the Meine l 0-0 band during aurora at Poker Flat, Alaska. Since both upper states hav e short lifetimes, compared to the inverse of the collision rate at heights of the emission, and the ratios of their excitation cross sections by elec tron impact is not sensitive to energy above 10 eV, it was expected that th eir emission rates should be strictly proportional. We have found that the brightness of the first negative 0-1 increases above the proportionality ra te during moderate auroral activity. After careful consideration of a numbe r 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 t he sunlit or twilight region. (C) 2001 Elsevier Science Ltd. All rights res erved.