Abstract
A five-channel interference filter photometer was used to make observations of the relative brightnesses of the First Positive Group N2 bands, the λ-3 914 N2+ band, the λ-5 577 [OI] line, and the First Negative O2+ bands in type-B red aurora. It was found that the time delay between the emission of the 1NG N2+ bands and the 1PG N2 bands was less than 0.1 second in disagreement with the O2−/N2+ charge neutralization mechanism for the enhancement of the First Positive Group bands.The lifetime of the O(1S) atoms emitting the green line was determined by the method of Omholt (1959) by comparing fluctuations in the emission of the green line with those of the N2+ bands. In type-B red aurora it was found that this lifetime corresponded to 0.48 ± 0.06 second as compared with 0.67 ± 0.06 second in normal aurora. This may indicate that collisional deactivation of the O(1S) state occurs in type-B red aurora and is one factor contributing to the reddening.The relative brightness measurements showed, for type-B red aurora compared with normal aurora, an appreciable intensification (~50%) of the 1PG emission compared to the 1NG N2+ bands. At the same time there was observed an average decrease of about 30% in the intensity of the green line compared to the 1NG bands.
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