OBSERVATIONS AND INTERPRETATION OF SPECTRA AND RAPID TIME VARIATIONS OF TYPE-B AURORA

Observations of type-B red and normal aurora were made with a high-speed multichannel photometer and a digital grating spectrometer. The ratio I(O2 + 1N; 2, 0 + 3, 1) I(N2 + 1N; 0, 3) measured in the 5200-5300 Å region with the spectrometer was found to increase by about 16% from normal to type-B aurora. This small change is difficult to reconcile with a height below 90 km for the red border. In the type-B aurora, λ 5577 was weakened by a factor between 1.9 and 3.8 while the ratio I(N2 1P; 5, 2) I(N2 + 1N) was enhanced less than 20%. Rapid intensity variations in the type-B lower border were observed in the λ 5577 and other channels of the photometer. A revised time dependent auroral excitation-ion chemistry model is used in an attempt to reproduce the observations. The observed weakening of λ 5577 could be produced at heights equal to or less than 100 km while the short observed time lag of λ 5577 on the N2 + 1N emission is easier to explain at 100 km than at 80 km. It is concluded that some type-B lower borders may occur near 100 km although it is recognized that there is good evidence rare deep crimson lower borders lie at 80 km or below. The mechanism for the excitation of O(1S) is considered in the light of these results. None of the mechanisms examined is satisfactory on the basis of currently accepted atmospheric models and quenching rate coefficients. © 1979.