Wavelike Oscillations in High Latitude Thermospheric Doppler Temperature
and Line-of-Sight Wind Observed Using All-Sky Imaging Fabry-Perot
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.