The early 2021 Sudden Stratospheric Warming as observed by ADM-Aeolus

Sudden Stratospheric Warmings (SSWs) are dramatic events where the usually-strong wind vortex around the edge of the polar stratosphere temporarily weakens or reverses, causing the polar temperature to rise by tens of Kelvin in just a few days. These events can trigger extreme winter weather outbreaks in Europe and North America, and are thus of significant scientific and practical interest. However, due to the major technical challenges involved in measuring wind from space, the changes in wind structure involved in an SSW have never been directly observed at the global scale, and our understanding of these changes has instead been developed through the use of point measurements, localised flight tracks and (primarily) computer models and assimilative analyses. Here, we exploit novel measurements from Aeolus, the first satellite capable of observing wind in the upper troposphere and lower stratosphere, to study this process observationally during the major January 2021 SSW. As the event is still ongoing at time of abstract submission, precise details of the changes seen in Aeolus data over the full event cannot be provided; however, data from the first full week of the SSW shows clear observational evidence in Aeolus data of significant and descending-with-time structural changes to the lower stratospheric flow, including reversal of the mean zonal flow, a clear shifting of the vortex centre to a location over northern Russia, and perhaps early evidence of a developing split of the vortex into two sub-vortices.