Observations of high-latitude lower thermospheric winds from Thule Air Base and Sondre Stromfjord, Greenland

Lower thermospheric winds have been determined from Fabry-Perot interferome ter (FPI) measurements of the Doppler shift of the 5577-Angstrom O(S-1) emi ssion over Thule Air Base (76.5 degrees N, 69.0 degrees W) and Sondre Strom fjord (67.0 degrees N, 50.9 degrees W), Greenland. These winds normally cor respond to the altitude of the peak of the airglow O(S-1) emission layer, n ear 97 km. The altitude ambiguity due to auroral contamination has been red uced by eliminating data when the intensity of the emission increases signi ficantly. Contamination by airglow emission of 5577-Angstrom O(S-1) origina ting from higher altitudes has been investigated by an FPI simulation code. The simulation results indicate that this latter emission may contribute a n anomalous diurnal oscillation to ground-based 5577-Angstrom, O(S-1) FPI m easurements of lower thermospheric wind. The agreement of diurnal phases be tween that deduced from the green-line measurements and that determined fro m simultaneous red-line observation supports this conclusion. The same simu lation applied to observations from Sondre Stromfjord shows Chat the upper layer contamination is much weaker and is not serious. Significant day-to-d ay variation is evident in the lower thermospheric wind field. Average neut ral winds are calculated, and a harmonic analysis is carried out to examine the major low-frequency wind components. The seasonal variations of these wind components are compared with radar data and model predictions. The obs ervations are generally in good agreement with model results. The compariso n between FPI and radar results also shows reasonable agreement. The semidi urnal amplitudes observed with the Sondre Stromfjord radar during the Lower Thermospheric Coupling Study (LTCS-1) and LTCS-2 periods are always greate r than the climatological values obtained from averaging FPI and Chatanika radar observations. This result shows the variability that can be expected when comparing "instantaneous" estimates of tidal parameters with climatolo gical results.