An extreme cold event over East Asia during early January 2021 and its links to the deformation of stratospheric polar vortex during sudden stratospheric warming

Abstract

In early winter of 2020/2021, East Asia experienced two extreme cold events (ECEs), during which a number of national stations in China reached the standard of ECE or broke records. The underlying dynamical processes of these record‐breaking ECEs are investigated using Modern‐Era Retrospective Analysis for Research and Applications version 2 reanalysis dataset. Results show that these ECEs were closely related to the sudden stratospheric warming (SSW) event. During 29 December, 2020–1 January, 2021 (the first ECE), the tropospheric polar vortex migrated to mid‐latitude East Asia and more planetary wave propagated into the stratosphere. Then, the stratospheric polar vortex weakened and extended to mid‐latitude East Asia from 2 January. And, a SSW event occurred on 5 January. The easterly zonal wind accompanied by the deformation of stratospheric polar vortex over East Asia tended to strengthen the East Asian trough via reflecting the planetary wave from the stratosphere to troposphere. Simultaneously, the southward shifting of the Ural ridge resulted in the extremely strong East Asian trough migrating southward, which led to the strengthening and southward migration of near‐surface anticyclonic circulation. Then, another ECE broke out during 6–7 January (the second ECE). Therefore, the ECE in early January was jointly caused by the combined effects of deformation of stratospheric polar vortex during SSW event and the southward shifting of Ural ridge. Further analysis suggested that about 8% of the total ECEs during 1980/1981–2019/2020 were related to the extension of stratospheric polar vortex to East Asia.

Coupling between maximum temperature and ozone levels in the lower stratosphere and extreme cooling events in Northeast China

“…The polar vortex perturbed by planetary waves produces a zonally asymmetric pattern in the SSW effects observed in air temperature, winds, total ozone content (TOC) and tropopause altitude (Thompson and Wallace 2000;Kolstad et al 2010;Kidston et al 2015;Kim and Kim 2021;Ding et al 2022). Because of quasi-stationary wave structure, the SSW influence is often manifested as a persistent extreme cold weather in certain regions, such as Northern Europe, northeastern North America or East Asia (Thompson and Wallace 2000;Tomassini et al 2012;Lehtonen and Karpechko 2016;Lü et al 2020;Butler et al 2020;Choi et al 2021;Rao et al 2021;Kolstad et al 2022;Zhang et al 2022;Liu et al 2023). We analyze regional extreme cooling events, which involve stratosphere-troposphere coupling but are not associated with the SSW.…”