Limited surface impacts of the January 2021 sudden stratospheric warming

Abstract

Subseasonal weather prediction can reduce economic disruption and loss of life, especially during “windows of opportunity” when noteworthy events in the Earth system are followed by characteristic weather patterns. Sudden stratospheric warmings (SSWs), breakdowns of the winter stratospheric polar vortex, are one such event. They often precede warm temperatures in Northern Canada and cold, stormy weather throughout Europe and the United States - including the most recent SSW on January 5th, 2021. Here we assess the drivers of surface weather in the weeks following the SSW through initial condition “scrambling” experiments using the real-time CESM2(WACCM6) Earth system prediction framework. We find that the SSW itself had a limited impact, and that stratospheric polar vortex stretching and wave reflection had no discernible contribution to the record cold in North America in February. Instead, the tropospheric circulation and bidirectional coupling between the troposphere and stratosphere were dominant contributors to variability.

The “Polar Vortex” Winter of 2013/2014

“…Similar experiments could be run with different regions within the troposphere as well (e.g., tropics vs. mid-latitudes). Indeed, Kautz et al (2020) and Davis et al (2022) performed such experiments to diagnose the roles that SPV variability played (or did not play) on extreme cold air outbreaks across Eurasia (Kautz et al, 2020) and the central US (Davis et al, 2022). Such experimentation may also help us understand better why predictability of the wintertime extratropical stratospheric circulation is limited to 2 weeks or less in operational subseasonal prediction systems (e.g., Domeisen, Butler, et al, 2020).…”

A new methodology for measuring traveling quasi-5-day oscillations during sudden stratospheric warming events based on satellite observations

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

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).…”