Investigating the Geophysical Drivers of Thermospheric Wave Activity via Scanning Doppler Imagers

The redistribution of energy and momentum within Earth’s thermosphere is partially carried by thermospheric waves. These waves may arise in the thermosphere either as a result of magnetospheric forcing from above or upward propagation from sources in the lower atmosphere. In order to better resolve wave excitation mechanisms, we have examined a large set of thermospheric wind observations to identify periods of strong wave activity. For each of these events, we have also identified the spatial and temporal distribution of forcing associated with auroral and magnetic activity, as well as the strength, direction, divergence, and vorticity of the background horizontal wind field. By constructing a clearer picture of the physical events that lead to these periods of heightened wave activity, we aim to build a statistical understanding of thermospheric wave origins and the consequential transport of energy and momentum.
This catalog of events is derived from observations taken by Scanning Doppler Imager (SDI) Instruments located in Alaska and Antarctica. These ground-based instruments view almost the entire sky with a cadence of several minutes. This field of view is divided into 115 look directions from each of which is obtained an optical spectrum of the 630 nm emission line, spanning roughly 10 picometers in wavelength with a resolving power in excess of 500,000. Fitting model emission profiles to the spectra returns estimates of Doppler spectral widths and Doppler shifts that provide temperature and wind estimates across the instrument’s field of view. Candidate wave signatures are extracted by applying high-pass filters to our wind and temperature time series in order to isolate periodic perturbations. Strong coherence between the densely sampled (both spatially and temporally) wind and temperature oscillations provides confidence in the interpretation that these perturbations are indeed signatures of waves.
This poster presents the results of our investigation into the dependence of wave activity on the forcing regime and describes the mechanisms that appear within our data to be most directly associated with strong wave activity in Earth’s middle thermosphere.