Observations of gravity waves in the OH airglow layer above Rothera
(68S, 68W) using a three-dimensional S-Transform analysis
Abstract
In this study, we apply the three-dimensional Stockwell Transform (3DST)
to a novel dataset, namely airglow imager data from Rothera (68S, 68W).
We use this approach to investigate small-scale high-frequency gravity
waves (GWs) in the hydroxyl (OH) airglow layer, at a height
$\sim$87 km in the mesosphere and lower thermosphere
(MLT). MLT GWs are often underrepresented in models, being parameterised
due to their small scale size and as such, the significant quantities of
momentum and energy transferred by these small waves are missed. Better
quantification of these waves is thus needed to support future model
development. We find that the 3DST can identify waves and extract wave
properties and their locations. Horizontal wavelengths are observed
ranging from 10 to 40 km and vertical wavelengths of 15 to 40 km, with
wave periods of 5 to 9 minutes, peaking at 7.5 minutes. These values are
consistent with previous studies. Group speeds are found to be non-zero
and large, implying that these GWs travel horizontally and fast. This
case study demonstrates that the 3DST can be applied to airglow imager
data and can successfully extract GW parameters. This is an important
step in automating GW analysis in airglow.