Extreme Cold Events from East Asia to North America in Winter 2020/21: Comparisons, Causes, and Future Implications

Abstract

Three striking and impactful extreme cold weather events successively occurred across East Asia and North America during the mid-winter of 2020/21. These events open a new window to detect possible underlying physical processes. The analysis here indicates that the occurrences of the three events resulted from integrated effects of a concurrence of anomalous thermal conditions in three oceans and interactive Arctic-lower latitude atmospheric circulation processes, which were linked and influenced by one major sudden stratospheric warming (SSW). The North Atlantic warm blob initiated an increased poleward transient eddy heat flux, reducing the Barents-Kara seas sea ice over a warmed ocean and disrupting the stratospheric polar vortex (SPV) to induce the major SSW. The Rossby wave trains excited by the North Atlantic warm blob and the tropical Pacific La Nina interacted with the Arctic tropospheric circulation anomalies or the tropospheric polar vortex to provide dynamic settings, steering cold polar air outbreaks. The long memory of the retreated sea ice with the underlying warm ocean and the amplified tropospheric blocking highs from the midlatitudes to the Arctic intermittently fueled the increased transient eddy heat flux to sustain the SSW over a long time period. The displaced or split SPV centers associated with the SSW played crucial roles in substantially intensifying the tropospheric circulation anomalies and moving the jet stream to the far south to cause cold air outbreaks to a rarely observed extreme state. The results have significant implications for increasing prediction skill and improving policy decision making to enhance resilience in "One Health, One Future".

Influence of Major Stratospheric Sudden Warming on the Unprecedented Cold Wave in East Asia in January 2021

“…The results of this study are consistent with those of our previous study (Si et al, 2021), which shows that the IOCP is the most direct and important atmospheric pattern responsible for extreme cold waves in East Asia in January 2016. The influences of SSW on this extreme cold wave in East Asia have also been confirmed by other studies (Zhang et al, 2021a;Yu et al, 2022). Moreover, the tropospheric dynamics also played an important role in the occurrence of this extreme cold wave.…”

“…The SSW event and displacement of the stratospheric polar vortex may be attributed to the increase in the poleward transient eddy heat transport in the troposphere. A poleward propagating Rossby wave on 26-28 December 2020 resulted in a heat intrusion from the North Atlantic into the Arctic region (Zhang et al, 2021a). The poleward heat intrusion excited a strong tropospheric Rossby wave propagating from the troposphere to the midstratosphere in late December 2020 (Fig.…”

“…The frequent occurrence of extreme cold events is of great concern for adaptation to a warmer world (Kuang et al, 2019). The impressive cold surges in the early winter of 2020/21, which led to recordbreaking low temperatures in central and eastern China, aroused widespread public concern (Dai et al, 2021;Zhang et al, 2021a;Zheng et al, 2021;Bueh et al, 2022;Yao et al, 2022). These extreme low temperatures are often transnational or even continental, while it is relatively mild in the Arctic region.…”

The Alternating Change of Cold and Warm Extremes Over North Asia During Winter 2020/21: Effect of the Annual Cycle Anomaly

“…Recent studies have revealed that before 15 January 2021, negative AO anomaly consistent with a weakened stratospheric polar vortex is responsible for cold events over East Asia (Zhang et al, 2021;Zheng et al, 2021), and its AC reached the minimum on 15 Jan 2021, which is speculated to be related to sign changes in the Asian SAT anomaly. In addition to the considerable contribution of Arctic stratospheric signals, winter climate variations over Asia can also be affected by variabilities in the tropical Pacific and North Atlantic sea surface temperature and the Arctic sea-ice concentration (e.g., Cheung et al, 2016Cheung et al, , 2018Yu et al, 2021;Zhang et al, 2021). As a result, the influence of other factors on changes in AC anomalies of SAT in Asia needs further investigation.…”

Preface to the Special Issue on Extreme Cold Events from East Asia to North America in Winter 2020/21

“…Zheng et al (2022a) first pointed out that the middle-and high-latitude, large-scale atmospheric circulation anomalies associated with the negative phase of the North Atlantic Oscillation (NAO), a strengthened Siberian High, an intensified Ural High, and a deepened East Asian Trough, were the direct reasons for the frequent cold surges in winter 2020/21. The analysis by Zhang et al (2022a) further indicated that the occurrences of the three striking and impactful extreme cold weather events across East Asia and North America during the mid-winter of 2020/21 resulted from the integrated effects of a concurrence of anomalous thermal conditions in three ocean basins and an interactive Arctic-lower latitude atmospheric circulation process, which were linked through and influenced by one major sudden stratospheric warming (SSW) event. Zhang et al (2022b) also demonstrated the major SSW event occurred at the beginning of January 2021 exerted an important influence on the extreme cold wave in East Asia through inducing the stratospheric warming signal to propagate downward to the middle to lower troposphere, which not only enhanced the Urals-Siberia blocking and the negative phase of Atlantic Oscillation (AO), but also shifted the tropospheric polar vortex off the pole.…”