Atmospheric gravity waves are a type of buoyancy wave that, on breaking or becoming unsteady, deposit their energy and momentum into the mean atmospheric flow driving atmospheric circulation. These waves are ubiquitous in the atmosphere. They are caused by sources mainly in the lower atmosphere; for example, storms, wind flow over mountains, and perturbations in the Polar Vortex. They are an important dynamical means of coupling throughout the atmosphere.
Global climate models do not accurately capture these waves. This can result in modelled temperatures being too cold, and wind speeds too fast in the Polar Regions. Although observations of these waves are needed to constrain their modelled representation, in the Polar Regions there is a paucity of observations, especially of the short-horizontal wavelength waves that have been shown to carry the most momentum.
The Antarctic Gravity Wave Instrument Network (ANGWIN) started as an idea between a few Antarctic scientists who were studying mesospheric (~ 87 km altitude) gravity waves using all-sky airglow imagers to share analysis techniques and to study the gravity wave field at sites around Antarctica. Through the collaboration of different countries and deployment of different instrumentation, ANGWIN has grown to include modelling work and observations across different atmospheric “spheres”, in both Polar Regions.
A type of gravity wave called a mesospheric bore, captured using an all-sky OH
airglow imager located at Halley, Antarctica. The wave structure can be clearly
seen entering the picture from the top right and progressing across the field of
view. Details about these kinds of waves can be found in Nielsen et al. .
Credit: ANGWIN community
At the third ANGWIN workshop (in 2016) the large range of ANGWIN activities and results from collaborations became fully apparent. Atmospheric Gravity Wave Science in the Polar Regions and First Results From ANGWIN is a joint special collection of JGR: Atmospheres and JGR: Space Physics which presents the main results from this workshop.
This special collection contains a range of observational and modelling results concerning gravity wave studies throughout the whole atmosphere (from the ionosphere to the troposphere) and across both Polar Regions.
Many of the papers are single site studies, which are either case studies or climatologies. These use a range of ground-based instrumentation (i.e. radars, radiometers, all-sky airglow imagers, lidars and radiosondes), satellites (i.e. NASA AIM measurements) and modelling work (e.g. a gravity wave ray tracing model, the Horizontal Wind Model and Unified Model). These papers illustrate how different the gravity wave field is across many sites and that the influence of the different gravity wave sources varies considerably, not just with season but also with latitude and longitude.
A highlight of the special issue is research that has resulted directly from early ANGWIN discussions: application of the same analysis software to different locations of airglow all-sky imager data. The work by Matsuda et al.  has provided a clear example of how data and analysis software sharing can yield new insights into a field of research.
They used four Antarctic sites and developed a new method of analysis (The M-transform) that can be applied to these airglow data. The results show how the phase velocity of mesospheric gravity waves varies at each site and how gravity wave power varies with latitude.
Moving forward ANGWIN is pursuing more collaborative research through data and software sharing.
By using the same analysis techniques on similar datasets we can build a more robust understanding of the variations and properties of the gravity waves field across the Polar Regions.
—Tracy Moffat-Griffin (email: [email protected]), British Antarctic Survey, UK; Mike Taylor, Utah State University, USA; Takuji Nakamura, National Institute of Polar Research, Japan; Damian Murphy, Australian Antarctic Division, Australia; Jose Valentin Bageston, National Institute for Space Research, Brazil; and Geonhwa Jee, Korea Polar Research Institute, South Korea