Perturbed profiles of oxygen nightglow emissions as observed by WINDII on UARS

Abstract

Perturbed profiles having multiple peaks in the O( 1S) green line, O 2(b 1∑ g +) Atmospheric (0–0) band, and OH (8–3) Meinel band P 1(3) line nightglow emissions in the mesopause region are studied using observations of the Wind Imaging Interferometer (WINDII) onboard the Upper Atmosphere Research Satellite (UARS). These profiles were frequently observed by WINDII over the study period of 1991–1997, comprising up to 40% of the observations in bins having certain latitudes and local times. The preferred locations and times for their occurrences coincide with steep emission rate gradients associated with the diurnal tide. The assumption of horizontal homogeneity in the WINDII data processing implies that the perturbed profiles may be caused by horizontal as well as vertical variations. A 1-D model is developed to simulate the horizontal variation of volume emission rate embedded in a Gaussian distributed emission profile. The model results show that the secondary peak in the vertical emission profile could be the reflection of a wave-like horizontal structure with wavelengths between 100 and 400 km. The features of the horizontal structures correspond to localized regions of gravity waves with extents up to 2000 km and lifetimes of one or more days. It is concluded that the WINDII perturbed emission profiles could be produced by horizontal variations induced by gravity waves with wavelengths between 100 and 400 km, and that these occur in preferred regions of steep emission rate gradients associated with the diurnal tide.