Atmospheric scattering effects on ground-based measurements of thermospheric winds

Abstract

Inherent in observations of thermospheric winds from the ground with the Fabry-Perot interferometer is the assumption that the measured Doppler shift is a property of the source medium viewed by the instrumental line of sight. However, ground based airglow observations in regions of weak airglow emission near large intensity gradients may be contaminated by scattered light. Light from areas where the emission is strong can be scattered by the lower atmosphere into the field of view of the observations. Thermospheric winds deduced from the observed Doppler shifts will then show apparent convergence or divergence with respect to the site of observation. Examples of this effect are found in observations by the Michigan Airglow Observatory station located near the auroral zone at Calgary, Alberta. Simulation calculations based upon an experimental model for a significant scattering atmosphere also showed results with either convergence or divergence in the apparent neutral wind field observed by the station.