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.

We present a new analysis technique for estimating 2D neutral wind pattern using data from a single Scanning Doppler Imager (SDI) or a combination of SDIs, incoherent scatter radars (ISR) and Fabry-Perot interferometers (FPI) within overlapping field-of-views. Neutral wind plays an important role in ionospheric electrodynamics and Ionosphere-Thermosphere coupling, by for example affecting the Joule heating rates and plasma transport. However, reliable and extensive measurements of the neutral wind are rather difficult to obtain. Pointwise measurements can be obtained with ISRs or FPIs, but these measurements can not provide 2D latitude-longitude maps of the neutral wind pattern needed in mesospheric studies. A Scanning Doppler Imager can measure the line-of-sight (LOS) component of the neutral wind in dozens of directions simultaneously. However, further modeling is needed to convert the LOS velocities into 2D velocity maps. Unfortunately these maps are far from unique, as perpendicular velocities (e.g. rotation around the measurement site) are not visible in the LOS data. This can be mitigated by combining data from several nearby SDIs, or a combination of SDIs, FPIs and ISRs. Our analysis technique is based on fitting the LOS data with special vector basis functions called Spherical Elementary Current Systems (SECS). In this approach the wind is naturally divided into curl-free and divergence-free components, and there is no need to provide any explicit boundary conditions on the wind pattern. We present several synthetic test scenarios as well as first results using data from SDIs located in Alaska. Using the synthetic test scenarios we further estimate optimal locations for 2 or 3 SDIs that could be located around the future EISCAT_3D radar system in northern Scandinavia.

2D thermospheric wind fields, at both E- and F-region altitudes within a common vertical volume, were made using a Scanning Doppler Imager (SDI) at Poker Flat, Alaska, during a substorm event. Coinciding with these observations were F-region plasma velocity measurements from the Super Dual Auroral Radar Network (SuperDARN), and estimations of the total downward and upward field-aligned current density from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). This combination of instruments gives an excellent opportunity to examine the spatial characteristics of high latitude ionosphere-thermosphere coupling, and how a process which is triggered in the magnetosphere (the substorm) affects that coupling at different altitudes. We find that during the substorm growth phase, the F-region thermospheric winds respond readily to an expanding ionospheric plasma convection pattern, whilst the E-region winds appear to take a much longer period of time. The differing response timescales of the E- and F-region winds is likely due to differences in neutral density at those altitudes, resulting in E-region neutrals being much more ‘sluggish’ with regards to ion-drag. We also observe increases in the F-region neutral temperature, associated with neutral winds accelerating during both substorm growth and recovery phases.