Impact of Ural blocking on winter warm Arctic-cold Eurasian anomalies. Part II: The link to the North Atlantic Oscillation

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.