Spectral signatures of the Earth's night airglow observed from the Space Shuttle

Abstract

This research extends an observation program that recorded the night airglow from a Tucson ground station using an imaging spectrograph known as GLO. GLO was designed at the Lunar and Planetary Laboratory of the University of Arizona to observe auroral and airglow emissions, and recorded midlatitude airglow data near equinox during Space Shuttle mission STS-69 in September 1995. GLO observations from the shuttle recorded the night airglow layer seen edge on at the Earth's limb. These observations from orbit exhibit a fundamentally different picture of the night airglow compared to observations from the ground. GLO data also represent the first simultaneous optical measurements of airglow emissions over the spectral range from 1150 to 9000 A, showing global emission variations in the night sky. Intensity variations are not correlated among emitting species, implying greater dynamism and more complex chemical interactions in the airglow than previously assumed. Although other researchers have described observations of organized waves and tides in the night airglow, these prior observations are sporadic or averaged over long time periods. The night sky intensity variations recorded by GLO do not exhibit any obvious relationship to atmospheric tides. They may instead be the result of a chaotic superposition of upward and downward vertical motions. This upwelling and subsidence may cause the decoupling of airglow emissions in the O2 Atmospheric band, the OH Meinel band, and the atomic oxygen green line at 5577 A. Emission enhancements with maxima-to-minima ratios of 4 to 12 depending on emitting species, have been observed in the GLO data. Emissions in the O2 Atmospheric band system and the OI (5577 A) green line show a greater dynamic range of variation than the OH Meinel band system. The chemistry along a limited line-of-sight can be explained by classical airglow chemistry, but only over a limited altitude range. Dynamic effects in the 80 to 100 km region are sufficiently chaotic to present mixed results when inferring chemical processes as a function of altitude.