An Update on Extraction of Wavelike Oscillations in Thermospheric Temperature and Line-of-Sight Wind Data Acquired by All-Sky Imaging Optical Doppler Spectroscopy

Time-series measurements of temperature and line-of-sight (LOS) wind from Earths thermospheric E- and F-regions were obtained using several all-sky imaging Fabry-Perot interferometers, also known as Scanning Doppler Imagers (SDIs). These instruments were located in both Alaska and in Antarctica. High-pass temporal filtering of the time-series measurements was used to remove spectral components corresponding to periods of two hours or longer. Some level of wave-like oscillations were detected in F-region winds during almost all times when the sky was clear and the instruments were operating correctly. Oscillations were also detected in F-region temperatures and E-region winds, but less frequently, due to signal-to-noise constraints. The all-sky field of view (FOV) was typically divided into 115 independent zones, and oscillations in wind and temperature were extracted from each of these zones. Amplitudes of oscillations in the LOS wind component were found to increase with increasing observing zenith angle, as expected for perturbations primarily in horizontal wind. Phase progressions were observed among oscillations associated with varying look azimuths and also with varying zenith angles. Highly time-synchronous perturbations with relatively large amplitudes were, at times, observed across the whole FOV. We interpret these as simultaneous responses to direct driving, and specifically not as signatures of propagating waves. F-region temperature and LOS wind oscillations were typically found to correlate well with geomagnetic activity. In cases where two or more nearby SDIs had overlapping FOVs they often recorded highly correlated wave activity. Lomb-Scargle analysis was performed to resolve the spectral distributions of the underlying oscillations. Wave spectra were observed to vary from zone to zone, indicating that the instruments can resolve variations in wave activity over the geographic regions observed. Wave periods seen at F-region heights were typically 80 minutes or more, whereas in the E-region a broader range of periods was observed, extending down to as short as 30 minutes.