Impact of Ural Blocking on Winter Warm Arctic–Cold Eurasian Anomalies. Part II The Link to the North Atlantic Oscillation

• Published in: Journal of climate Vol. 29; no. 11; pp. 3949 - 3971
• Main Authors: Luo, Dehai, Xiao, Yiqing, Diao, Yina, Dai, Aiguo, Franzke, Christian L. E., Simmonds, Ian
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.06.2016
• Subjects: Amplification; Anomalies; Atmospheric forcing; Case studies; Classification; Cold; Displacement; Ice; Marine; North Atlantic Oscillation; Ocean-atmosphere system; Polar environments; Temperature; Ural blocking; Wave packets; Wave propagation; Wave trains; Winds; Winter; Zonal winds; Eurasia; Arctic region; Europe; China; Russia; AN, North Atlantic; Russia, Ural Mts; AE, East Atlantic; AN, North Atlantic, North Atlantic Oscillation; PNE, Eurasia; China, People's Rep
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-15-0612.1

In Part I of this study, the Ural blocking (UB)-induced amplification role of winter warm Arctic–cold Eurasian (WACE) anomalies has been examined. It was found that the long-lived UB together with the positive North Atlantic Oscillation (NAO⁺) significantly contributes to the amplification of the WACE pattern. The present study examines how the UB variability affects quasi-biweekly WACE (QB-WACE) anomalies and depends on the NAO⁺ and North Atlantic conditions by classifying the UB based on a case study of a cold event that occurred over southern China in January 2008. A composite analysis during 1979–2013 shows that the QB-WACE anomalies associated with the UB that often occur with the NAO⁺ are strong and influenced by the North Atlantic jet (NAJ) and zonal wind strengths over Eurasia. For NAO⁺-related UB, the QB-WACE anomaly depends strongly on the location of UB, and the UB anomalies lag the NAO⁺ by approximately 4–7 days. The strength of the NAJ determines whether the combined NAO⁺ and UB anomalies exhibit a negative East Atlantic/West Russia (EA/WR⁻) pattern, while the region of weak zonal winds over Eurasia and the zonal extent of the NAJ dominate the location of UB. For southward-, eastward-, and westward-displaced UBs associated with a strong NAJ, the NAO⁺ favors the UB with a southward-displaced QB-WACE anomaly through wave train propagation like an EA/WR⁻ pattern. Eastward- and southward-displaced UB anomalies induce similarly displaced cold anomalies with intrusion into southern China. However, for a northward-displaced UB, this happens without pronounced EA/WR⁻ patterns because of a weak NAJ and is accompanied by a northward-displaced QB-WACE anomaly.