Dynamical and surface impacts of the January 2021 sudden stratospheric warming in novel Aeolus wind observations, MLS and ERA5

Abstract

Abstract. Major sudden stratospheric warmings (SSWs) are extreme dynamical events where the usual strong westerly winds of the stratospheric polar vortex temporarily weaken or reverse and polar stratospheric temperatures rise by tens of kelvins over just a few days and remain so for an extended period. Via dynamical modification of the atmosphere below them, SSWs are believed to be a key contributor to extreme winter weather events at the surface over the following weeks. SSW-induced changes to the wind structure of the polar vortex have previously been studied in models and reanalyses and in localised measurements such as radiosondes and radars but have not previously been directly and systematically observed on a global scale because of the major technical challenges involved in observing winds from space. Here, we exploit novel observations from ESA's flagship Aeolus wind-profiler mission, together with temperature and geopotential height data from NASA's Microwave Limb Sounder and surface variables from the ERA5 reanalysis, to study the 2021 SSW. This allows us to directly examine wind and related dynamical changes associated with the January 2021 major SSW. Aeolus is the first satellite mission to systematically and directly acquire profiles of wind, and therefore our results represent the first direct measurements of SSW-induced wind changes at the global scale. We see a complete reversal of the zonal winds in the lower to middle stratosphere, with reversed winds in some geographic regions reaching down to the bottom 2 km of the atmosphere. These altered winds are associated with major changes to surface temperature patterns, and in particular we see a strong potential linkage from the SSW to extreme winter weather outbreaks in Greece and Texas during late January and early February. Our results (1) demonstrate the benefits of wind-profiling satellites such as Aeolus in terms of both their direct measurement capability and use in supporting reanalysis-driven interpretation of stratosphere–troposphere coupling signatures, (2) provide a detailed dynamical description of a major weather event, and (3) have implications for the development of Earth-system models capable of accurately forecasting extreme winter weather.

On the derivation of zonal and meridional wind components from Aeolus horizontal line-of-sight wind

“…Nevertheless, it is already used in the community (e.g. preprint of Wright et al, 2021, andChou et al, 2021) and we will show later that under certain conditions it provides reasonable estimates for the zonal wind.…”

“…Zagar et al, 2021), sudden stratospheric warmings (SSWs; e.g. Wright et al, 2021), or the quasi-biennial oscillation (QBO; e.g. Banyard et al, 2021b).…”

A new methodology for measuring traveling quasi-5-day oscillations during SSWs based on satellite observations

“…To be distinguished from the SSW in February 2018, the SSW with the onset date of December 28, 2018, is discussed as the "2019 SSW" in this study. The SSWs before 2013 have been widely studied in previous studies (e.g., Choi et al, 2019;Charlton and Polvani, 2007;Butler et al, 2017), and details of the three major SSWs from 2018 to 2021 can be referred to many recent reports (e.g., Rao et al, 2018Rao et al, , 2020Rao et al, , 2021Wang et al, 2019;Davis et al, 2022;Okui et al, 2021;Wright et al, 2021). propagating before the SSW onsets (e.g., Gong et al, 2018;Yu et al, 2022).…”

“…Previous studies usually ignored the effect of SPWs when obtaining the amplitudes of Q5DOs from satellite observations (e.g., Gong et al, 2018;Qin et al, 2021). Nevertheless, both westward and eastward Q5DOs have been frequently reported during SSWs in recent years (e.g., Pancheva et al, 2018 al., 2021;Wang et al, 2021;Yu et al, 2022). Thus, it is necessary to understand the real physics of the enhanced Q5DOs during SSWs and their relationships with SPWs.…”

How Well Are Sudden Stratospheric Warming Surface Impacts Captured in CMIP6 Climate Models?

“…If cold conditions in Siberia extend to western Europe, they can be responsible for significant weather extremes with high societal impact, with concomitant implications for health and infrastructure. One such event was the extreme cold snap in 2018 (e.g., Karpechko et al., 2018; Rao et al., 2018), and an SSW in January 2021 was followed by a prolonged cold spell in western Europe, extreme cold and snow in Texas, and snow in Athens (Wright et al., 2021).…”