Rajan Itani

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Multiple years of thermospheric wind and temperature data were examined to study gravity waves in Earth’s thermosphere. Winds and temperatures were measured using all-sky imaging optical Doppler spectrometers deployed at three sites in Alaska, and three in Antarctica. For all sites, oscillatory perturbations were clearly present in high-pass temporally filtered F-region line-of-sight (LOS) winds for the majority of the clear-sky nights. Oscillations were also discernible in E-region LOS wind and F-region Doppler temperature, albeit less frequently. Oscillation amplitudes correlated strongly with auroral and geomagnetic activity. Observed wave signatures also correlated strongly between geographically nearby observing sites. Amplitudes of LOS wind oscillations were usually small when viewed in the zenith and increased approximately with the sine of the zenith angle – as expected if the underlying motion is predominantly horizontal. The SDI instruments observe in many look directions simultaneously. Phase relationships between perturbations observed in different look directions were used to identify time intervals when the oscillations were likely to be due to traveling waves. However, a portion of the instances of observed oscillations had characteristics suggesting geophysical mechanisms other than traveling waves – a recognition that was only possible because of the large number of look directions sampled by these instruments. Lomb-Scargle analysis was used to derive examples of the range of temporal periods associated with the observed LOS wind oscillations. F-region wind oscillations tended to exhibit periods typically ranging from 60 minutes and above. By contrast, E-region wind oscillation periods were as short as 30 minutes.