Longer Duration of Extreme Cold Events Over East Asia Affected by the Stratospheric Polar Vortex Extension

Abstract

Using long-term reanalysis data, extreme cold events (ECEs) over East Asia are categorized into long-duration ECEs (L-ECEs, lasting more than 7 days) and short-duration ECEs (S-ECEs, lasting 3–7 days) according to the duration of ECEs during boreal winters from 1959/1960 to 2019/2020. Our results show that L-ECEs over East Asia exhibit greater intensity, higher frequency, and longer persistence than S-ECEs. On annual average, L-ECEs are 1.8 K colder, contribute over 60% of total ECE days, and dominate in longer durations, persisting beyond day 5 and lasting up to 12 days. L-ECEs in East Asia are attributed to the extension of the stratospheric polar vortex (SPV) toward the Atlantic-Euro region. This SPV extension tends to enhance the Atlantic-Euro trough, which is coupled with a strengthened and persistent Eurasian teleconnection pattern and a strengthened Ural ridge and East Asia trough during the decay of ECEs (after day 3). The strengthened East Asia trough, accompanied with cyclonic circulation, facilitates the transport of cold air from higher to lower latitudes. This process makes the ECEs more persistent and longer in duration, potentially developing into L-ECEs. The findings of this study provide valuable insights into the linkages between the extension of the SPV and ECEs over East Asia from a long-term climate statistics perspective instead of relying solely on case-by-case analysis. This study may offer a valuable new predictor for forecasting long-lasting ECE events over East Asia.