Deducing composition and incident electron spectra from ground‐based auroral optical measurements: Variations in oxygen density

Abstract

Ground‐based optical observations have been made of the N2+ (4278 Å), O I (6300 Å), O I (7774 Å), and O I (8446 Å) auroral emissions. Data were collected on 12 nights from 1984 to 1986 at observatories in the auroral zone and were analyzed using the Strickland et al. (this issue) auroral electron impact excitation model results. It was found that during quiet geomagnetic conditions these data were consistent with O densities, at altitudes from 110 to 200 km, less than one‐half the densities given in the Jacchia 1977 or MSIS 1983 models. During highly disturbed periods such as during the great February 1986 storm, where Ap reached 202, the O density decreased an additional factor of 8. During the same storm the O2 density increased by less than a factor of 2 from its quiet value. These data also imply that the decrease in the O density is larger at higher altitudes during disturbed periods, in qualitative agreement with the heating model of Hays et al. (1973).