Dayglow O2 Atm emission observations at equatorial and low latitudes by WINDII

Abstract

Observations of the dayglow O2 Atm (0,0) band emission by the WINDII experiment on the UARS for 1992 and 1993 have been employed to study the emission's temporal and spatial variability at equatorial and low latitudes encompassing the latitude range of 30°N to 30°S. The WINDII O2 Atm (0,0) dayglow volume emission rates (VER) allowed day-to-day examination of their morphology over the altitude range from 80 km to 120 km altitude. The dayglow O2 Atm (0,0) VER revealed double-layered structures with peaks at about 88 km and at 98 km. Most of the O2 Atm (0,0) VER had their peak altitude at 88–92 km and their zonal variability to a great extent reflected the effect of diurnal tides, both seen in the elevated single peak on individual days and asymmetric with respect to the local noon. The upper peak at 98 km exhibited strong dependence on the local time and solar zenith angle, often centred around local noon, but independent of season as it became dominant or comparable to the lower peak for 12 LT ± 3 h. No upper peaks were observed before 8 LT and after 16 LT. Distinct wave-4 like signatures were observed embedded in the lower peak layer, at 88–90 km altitude. The double-layered structures when present often indicate a wave-4 like perturbations, more pronounced at the upper peak at 98 km. In the context of the double-layered structures observed and reported herein the ubiquitous presence of wave-4 perturbations suggest that these signatures result from tidal advection of [O] and the background atmosphere (N2, O2 and temperature).