Exploring Sources of Gravity Waves in the Southern Winter Stratosphere Using 3‐D Satellite Observations and Backward Ray‐Tracing.

During austral winter, the southern high latitudes has some of the most intense stratospheric gravity wave (GW) activity globally. However, producing accurate representations of GW dynamics in this region in numerical models has proved exceptionally challenging. One reason for this is that questions remain regarding the relative contributions of orographic and non‐orographic sources of GWs here. We use three‐dimensional (3‐D) satellite GW observations from the Atmospheric Infrared Sounder in austral winter 2012 in combination with the Gravity‐wave Regional Or Global Ray Tracer to backward trace GW rays to their sources. We trace over 14.2 million rays, through ERA5 reanalysis background atmosphere, to their lower atmospheric sources. We find that GWs observed thousands of km downstream can be traced back to key orographic regions, and that on average, all waves (orographic and non‐orographic) converge meridionally over the Southern Ocean. We estimate that across this winter, orographic sources contribute around ∼ ${\sim} $ 5%–35% to the total momentum flux (MF) observed near 60° ${}^{\circ}$S. The remaining proportion consists of waves from non‐orographic sources, which although typically carry lower MF, the large spatial extent of non‐orographic sources leads to a higher overall contribution. We also quantify the proportion of MF traced back to different regions across the whole southern high latitudes area in order to measure the relative importance of these different regions. These results provide the important insights needed to advance our knowledge of the atmospheric momentum budget in the southern high latitudes. Plain Language Summary: Just like the ocean, our atmosphere contains waves which transport energy and momentum. These atmospheric waves, known as gravity waves (GWs), strongly influence large‐scale wind patterns but are hard to represent in climate models. The Southern Hemispheric stratosphere has some of the strongest GW activity on our planet and accurately representing this region in models has proved exceptionally challenging. Further, inaccurate representations of gravity waves can lead to major model biases. Here, we use satellite observations of stratospheric GWs and, using new methods, identify GWs and measure GW amplitudes, wavelengths, and directions. We then use these observations in combination with a ray‐tracing model to track observed GWs back to their sources near the ground. This approach means that, for the first time, we are able to produce systematic estimates of the relative contribution of different wave sources to the observed stratospheric activity in the southern high latitudes. Key Points: We use gravity wave properties derived from stratospheric satellite observations as input to a backward ray‐tracing modelRay‐tracing reveals that gravity waves observed at all longitudes around the Southern Ocean converge to 60°S as they propagate upwardWe quantify the momentum flux (MF) from different regions, finding that, in winter 2012, over half of the MF is traced back to the ocean [ABSTRACT FROM AUTHOR]