An inversion technique to recover lower thermospheric winds from space -borne remote measurements of (OI) 5577 angstroms.

Abstract

A new wind inversion technique that I developed to obtain neutral wind profiles from space-borne Fabry-Perot Interferometer (FPI) measurements of atmospheric airglow is presented. This generalized numerical technique is applied to (OI) 5577 A measurements taken with the FPI on board NASA's Dynamics Explorer-2 (DE-2) satellite to obtain wind profiles in the lower thermosphere (altitude range: 90 km to 150 km). DE2-FPI was the first satellite-borne instrument with sufficient spectral resolution to recover wind (and temperature) information from atmospheric emissions. An inversion technique must be applied to retrieve true wind profiles from space-borne (OI) 5577 A measurements because the non-local nature of this emission causes information to be averaged over altitude. As a precursory step to the wind inversion, I developed two brightness inversion techniques to recover the (OI) 5577 A volume emission rate profiles. Both the wind and the brightness inversion techniques were assessed for statistical and systematic errors using a DE2-FPI numerical simulator, also developed here. With this inversion method, it was possible to retrieve lower thermospheric winds with an accuracy of up to $\sim$$\pm$10 m/s. It was also shown that 5577 A volume emission rate profiles for both night-glow and day-glow can be successfully retrieved if constrained to Chapman layers. A preliminary study of the polar E-region wind field was conducted; inverted, binned and averaged polar DE2-FPI data was compared with the wind fields predicted by the National Center for Atmospheric Research - Thermospheric General Circulation Model (NCAR-TGCM) and the University College London - Thermospheric General Circulation Model (UCL-TGCM). The measured lower thermospheric wind field showed significantly stronger winds than model predictions, with less of an inclination toward the classic polar two cell pattern. Finally, an experiment was conducted to compare ground-based measurements of lower thermospheric winds made with an FPI and an incoherent scatter radar at the Sondre Stromfjord, Greenland facility. It was found that the ideal geophysical conditions required by the two instruments were almost mutually exclusive for this particular measurement. The necessary conditions for making simultaneous measurements were identified and confirmed by obtaining several hours of observations during a period exhibiting such conditions.