Tropical and Polar Oceanic Influences on the Cold Extremes in East Asia: Implications of the Cold Surges in 2020/2021 Winter

• Published in: Journal of marine science and engineering 2022-08, Vol.10 (8), p.1103
• Main Authors: Tan, Xiaoyu, Zhong, Linhao, Mu, Lin, Gong, Zhaohui
• Format: Article
• Language: English
• Subjects: Circulation; Clustering; Cold; Cooling; Cooling effects; East-Asia cold surge; El Nino phenomena; Ice; Ice cover; Influence; La Nina; Latitude; Modes; Phase transitions; Probability; Sea ice; Sea surface; Sea surface temperature; sea-ice melting; Surface temperature; synergy effect; Temperature; tropical ocean; Variables; Wave packets; Wave trains; Winter
• ISSN: 2077-1312; 2077-1312
• DOI: 10.3390/jmse10081103

East-Asia winter cooling and the associated atmospheric and oceanic influences were investigated based on the wintertime daily temperature and circulation fields during 1950–2020. Both the case study on the 2020/2021 cold surge and the large-sample clustering in the recent 71 winters extracted similar circulation signatures for East-Asia cooling, which are featured by the blocking-related anticyclonic circulation in North Eurasia, large-scale mid-to-high-latitude wave trains, decrease in the sea surface temperature (SST) in tropical Pacific, and the sea-ice cover (SIC) reduction in the Barents and Kara Seas (BKS). From the joint clustering of Eurasian circulation and temperature, two circulation modes that have a cooling effect on East Asia account for 41% of winter days. One of the two modes is characterized by the cyclonic circulation over Northeast Asia coupled with a southward-extending negative-phase Arctic Oscillation (AO−), whose cooling effect is mainly concentrated in central Siberia. The other cooling mode, featuring an anticyclonic circulation over the Urals and AO+ in middle-to-high latitudes, has a relatively stronger cooling effect on lower latitudes, including Mongolia and North China. In general, the occurrences of the mode with warming/cooling effect on East Asia show an overall downward/upward trend. The two cooling modes are significantly influenced by the La Niña-type SST anomaly and reduced SIC in BKS through large-scale wave trains, of which the tropical oceanic forcing mainly acts as a climatic background. Furthermore, the polar forcing is more tightly bound to internal atmospheric variability. Therefore, the tropical SST tends to exert impact over a seasonal scale, but the SIC influence is more significant below the intraseasonal scale; moreover, the synergy between the tropical and polar oceanic forcing can increase the East-Asia cooling days by 3–4% and cold extremes by 5%, mainly through enhancing the AO-related circulation mode.