Hyperspectral imaging of the night airglow layer from the shuttle: A study of temporal variability

Abstract

The temporal structure of the nightglow layer at the Earth's limb was monitored by the Arizona Airglow Experiment (GLO) from the space shuttle Endeavor throughout its 12‐day STS‐69 mission in September 1995. The GLO is a wideband long slit spectrograph or hyperspectral imager that views the Earth's limb at up to 24 contiguous tangent altitudes. All 24 spectra are recorded simultaneously from a single column of gas across the limb. Hyperspectral images of four emissions, O2(0,0), O2(Hz), O I(557.7), and OH(6,2), were constructed for analysis of the temporal condition of the nightglow layer along the orbit. It was found that the emission intensity of the major emitters, O2(0,0) and OH(6,2), were modified by factors of up to 3 by upward and downward transport of the mesospheric constituents through the 90–100 km region of the mesosphere. Significant variations in intensity were found associated with vertical transport of mesospheric cells 2000–5000 km in horizontal extent. The active cells are present for less than a day. Downward transport was signified by weakening of the OH(Meinel) emission and strengthening of the O2 and O I(557.7) emissions. Upward transport regions were outlined by enhancements in the OH(Meinel) and a second source of O2(atmospheric) emission. It was found that transport of low‐level mesospheric composition into the nightglow emission altitude region controls the nightglow spectral content. The atomic oxygen concentration above 100 km was found to be constant throughout the observational sequences and consequently not responsible for nightglow variability. An atmospheric interaction with the upward transported composition was detected. This interaction is likely to be with atomic oxygen that appears to be depleted following downward transport of the lower mesospheric composition. The OH emission is a true signature of mesospheric dynamics. Therefore this analysis initiates a new approach for monitoring mesospheric dynamics. Re‐analysis of archival data is recommended to detect the OH signature identified here. Collaborative ground‐based and space‐based overflight observational opportunities will be important to understanding the driving mechanism that initiates the vertical transport.